When a player decided to play a champion fighter they decided their PC was not going to cast spells. When they chose to play a druid the decided their PC was not going to wear metal armor.
Not necessarily. The Champion Fighter can still aspire to cast magic, can still take Magic Initiate, and can even jump into battle and try to replicate their Wizard's casting. They'll fail, but it's fully up to the character if they want to try. They're not going to explode (unless the DM wants to rule that their failed emulation leads to the casting of a failed Fireball and blow themselves up).
Someone that chooses to play a Druid does not necessarily choose not to wear metal armor. At most it's a tenet, and one that has no penalty for breaking. Applying a penalty would be a house rule, because the Sage Advice is official material, and explicitly states there is nothing within the game rules stopping the Druid from wearing the armor besides personal choice. If that Druid makes a contrary decision, there is nothing stopping them except a DM applying a house rule, one which has no basis for application, unlike rules such as with the Paladin's oaths.
A DM can always set up a situation the PCs can't win, just like they can always set up alternatives. It doesn't matter if that situation is a group of 1st level characters fighting a tarrasque, the only possible way to get out of a situation is for the champion fighter to cast teleport or the druid wearing metal armor. It's a DM choice to **** over the player because of their chosen class and restrictions.
And the point is, a character having to conflict their ideals against the situation in front of them is not a "no-win" situation. It's a conflict of interests for the character that forces them to weight cost versus outcome, but one they ultimately get to decide, and is not something that literally prohibits them from participating. A Paladin of Devotion opposes lying, but they can do it if they think it's the right course of action. Putting a Paladin of Devotion into a situation where lying will save many lives, or a Druid into a situation where putting on a suit of armor will complete their mission, is not comparable to expecting a Fighter to cast a spell they don't have access to.
All rules are optional. If you want druids in your campaign to wear metal armor, change the rule. I choose to follow the rules.
Considering Sage Advice is as official as the PHB, it's not a change in the rule to say Druids can wear metal. It is stated quite clearly that nothing stops them from doing it except personal choice. As soon as that choice changes, they're now wearing metal and nothing happens. Contrary to popular belief, they are quite clear in stating they do in fact not explode.
Uhhh... You are aware that those blurbs tend to list many different types in those descriptions? So, say, for instance the line about how critical the god is and the not follow specific divine arent at odds, just different options, right?
The blurbs often do give varying options, but the ones I listed do not. They are direct and to the point, and do not offer varying opinions. For example, the Monk description explicitly states that those who leave their cloister take their work seriously. It doesn't say they
usually take it seriously, or that they
typically take it seriously, it says they take it seriously. When it says they care little for material wealth and are driven by a greater mission, it doesn't say they
usually are, it just says that
as a rule, they are.
Nobody enforces these, however, as they are just story elements of the class and do not inflict any mechanical restrictions if not followed. The Sage Advice says that the Druid tenet is the same way, but people ignore this because of where it appears one block later in the class's description.
See at this point it feels more like "hostile reading" looking for how it can be misconstrued instead of what it means.
It's easy to misconstrue something when there's no explanation given.
As for devotion psladins, again, deception as a skill is not just for lying. Its also about hiding one's intent. So a high deception character might never lie but have a poker fsce from hell.
It doesn't matter if it's not just for lying. A Devotion Paladin can lie with Deception. Nothing stops them from doing it at any point in time, and if they do, they're still a Paladin of Devotion. Now in this specific case there is a lore blurb that tells the DM what they should consider doing if a player chooses to ignore their tenet, so it's not a house rule to enforce punishments that match with what is given. Druids, however, are explicitly stated in Sage Advice to have no such restrictions or punishments, because there is nothing within the game system preventing them from wearing metal armor.
Also, they don't need to be trained in the Deception skill to use it. Skills can be used untrained, you just won't get the proficiency bonus.