The issue is that what one person finds to be a loophole, another might not. For example, you say it's a loophole to try and circumvent the cost of Find Familiar, but literally the purpose of foraging skills and crafting tools is to reduce or bypass costs. Crafting your own armor cuts the cost in half, and if you also spent the necessary time in a mine to gather your own raw materials, it could reduce the cost to zero. Foraging reduces the cost of eating to zero because you don't need rations. A Healer's Kit costs 5GP, so should be craftable in a day, and it shouldn't be unexpected that a player taking a background to gain Nature, Survival, and proficiency in Herbalism, then spend a feat to gain Healer, would expect they can spend 8 hours crafting it in town for 2.5GP, or to be able to spend a bit more time out of town gathering their own ingredients to cut that cost to 0GP, so long as they had sufficient time to both craft it and gather the materials.I think this post sums up that we simply think differently. Here in the UK we have a saying 'it's just not cricket' - referring to the 'spirit' of a contest. The idea being that traditionally you are meant to play honestly and not try to push your luck, it's why we get annoyed here in the UK when sportsmen try to fool an official, eg a soccer player diving to win a penalty, or an American footballer claiming a catch when the ball is clearly not under control... we generally consider such behaviour to be unacceptable. It might be judgmental of us, or old-fashioned, but it's a general part of the British psyche.
It's the approach I use when playing D&D, I'm a firm but fair DM who tries to work within the spirit of the game with my players, and I expect the same in return. I have the same approach when playing a character, work with the DM, not against him. Work with the setting. Try not to push the boundaries.
Thus in the case of lawyer-style arguments regarding precise RAW language, for me it's the spirit of the rule that matters, NOT technicalities over preciseness of wording.
Trying to get around component costs of Find Familiar, trying to get around the 'no metal armour' restriction for Druids (along with other issues such as players trying to get around Drow sunlight sensitivity, etc) all come under this 'spirit of the game' heading. And thus my robust response when people have the approach advocated by yourself (and Maxperson). It's an unpleasant style of play, it derails sessions, it's disrespectful to Dm and fellow players, and the game is simply better for the group as a whole if it is avoided... so don't do it. And if you see this approach in AL games - I've played a couple, and I never saw this happen - then it's another reason to avoid them.
(my problem player I mentioned above was not British)
If all of the above is true, there's no reason why a player should not be able to do this with Find Familiar. Personally I'd find it silly if a DM told me I was just trying to loophole the system if I went out of my way to obtain all of the skills and tools built into the system for that purpose, all in order to utilize them for that purpose. Whether they utilize it to bypass food costs, bypass armor costs, bypass ammunition costs, etc, etc, that's what they're there for. In the case of your example, the issue definitely wasn't someone trying to loophole the system, but rather a whole other can of worms in terms of maturity and actually understanding the mechanical implications of the rules they were trying to utilize.
As for the Drow example, there's tons of ways to get around it that don't require anything exceptional. Use spells and cantrips that require a saving throw instead of an attack roll, utilize heavy obscurity, shade, or the Darkness spell, or otherwise apply disadvantage to any part of the battlefield that you're on if in direct sunlight, since you have disadvantage anyway. The sensitivity also shouldn't provide much penalty too often when it comes to detecting enemies, because it only applies to sight, and you can still hear a hidden enemy if they're moving. If they're in direct sunlight, you don't get further penalty for attacking them while unable to see them, so long as you can pinpoint them by sound, because you can't get double disadvantage. Unless the enemy is somehow in direct sunlight (which will actually often not be the case, since in order to be hidden they need to be behind something obstructing line of sight, which usually will block off direct sunlight), or the Drow is in direct sunlight (which he can bypass during travels by staying in the party's wagon), and the enemy is remaining stationary as to not need to move silently, there is no reason why the Drow cannot ignore most of the penalties. It absolutely should not be considered bad for the player to utilize the nuance of an ability and how it applies in actual play mechanics in order to mitigate its severity on their character. That's not using loopholes; it's smart gameplay.
And to repeat earlier points, this isn't a matter of just precise RAW language. The issue here is the "spirit" of the rule is that it's just a taboo, and is a tag on from previous editions, with no mechanical implications, going so far as to even grant the Druid proficiency in all medium armors (metal included). If the spirit of the rule was that they have a reason as to why they can't wear metal, the Sage Advice could have clarified this, but instead they clarified there is no such reason, which is good, because fits in the spirit of the game in terms of player choice. All class lore is within the spirit of the rules, but most class lore is ignored at most tables unless there's a mechanic that applies to ignoring it. How often do you see a DM force a Warlock's pact into their game, or a Monk's monastic past, force their Cleric to choose a deity (in systems that don't penalize not doing it), or tell a Paladin they can't choose to ignore their oath? Far less often than they allow a Druid to ignore elements of their lore. Sage Advice clarified that a Druid has nothing stopping them from putting on the armor, so if a character's backstory is built around the concept of being a Druid that focuses on stone and metal (I don't personally see that as unlikely for a Mountan Dwarf Circle of Land (Mountain) Druid), or a Druid that has decided that the old ways are silly and that they need to get with the times (much as a Cleric can denounce the worship of deities for a variety of reasons), I'd say the DM is the one being a rules lawyer by saying that the player can't make a decision because of a single unclarified (without Sage Advice) lore blurb saying they will not do it due to a belief system that by nature of the game should be able to change at any time anyway. Again, every other character can do it at any time, without reason, so why can't a Druid do it with reason?
If we're going to enforce the lore of the Druid to the "nature of the class", especially if going as far as to utilize the original lore to do it, I'd say that Druids don't belong in 99% of adventuring parties at all, as most parties aren't acting "in the spirit of the Druid class". They're all about defending nature, and shunning civilization (eww, no metal please, that's a civilization thing), so what the hell are they doing with an adventuring party that's taking on a mission to protect a human settlement from goblins? Why would they ever take a job for payment by the king? Why would they ever protect a kingdom? Why do they care if there's bandits in or out of town? Why are they going to help the elves take out the kobolds? What do they care about the kidnapped or eaten children? Why would the canonical Druid care about anything that is not simply a direct assault on nature?
The only way for these things to make sense is that the player character is an exception to the typical Druid's overzealous beliefs. This is why I would personally call it rule lawyering, and not in the spirit of the game in the state it's currently played, for the DM to force the player's actions (and even possible backstory) based on outdated lore mechanics that aren't even addressed in this edition.