RAW doesn't allow it, though. RAW requires it be something that Aragorn could actually help with in order to grant advantage, which as you note he cannot help Legolas in thr above situation.
My position isn't regardless of RAW. My position is RAW.
You may very well be correct, but it's obviously debatable because, well, people are debating it. I personally try to avoid "it does/doesn't make sense" as a basis for rulings when I run the game, because it basically boils down to "DM may I perform X action" scenarios. I don't want my players second guessing their own actions based on whether or not I'd allow it based on my perceptions of reality (which are inherently flawed because I can only perceive 0.0035% of the eletromagnetic spectrum, lol).
At any rate, if a DM wants to allow people to assist each other with Perception checks, it's their prerogative to do so, and it's not even wrong ("rulings not rules" is what WotC keeps saying). It's just different.
I find it eyebrow raising, I can only assume you find it patently ridiculous, but others apparently do not. With regards to roleplaying games in a fictional space, I think everyone has something that goes beyond the pale- some people hate the idea that a high level Fighter can fall two miles and not die, others point to Vesna Vulović. Some people can't see how someone could wield a quarterstaff in one hand as one could a spear, others are perfectly happy allowing staff and shield users to employ Polearm Mastery. I could go on, but the point is made. Rules as Written is no longer king, which makes discussions about rules incredibly frustrating, as the foundation of modern D&D wasn't built on bedrock, but something more akin to marshy ground or sand. People are legitimately allowed to say "I don't see it that way" (and really, they always have been able to), and nothing, not the sacred text, not the prophets who write it, nor the words of people who have been playing and running games for half a century (or longer!) is likely going to change their mind.
The bottom line is, there are penalties for relying on darkvision alone. Some people don't like them, others find it tedious to use them. That doesn't mean they don't exist, whether you can gain advantage on Perception checks or not. That makes it fairer than say, 3e darkvision. It's a trade off if you don't want to faff around with torches, lanterns, and 11' poles, just as taking the light cantrip or casting continual flame inside a scroll tube to make a crude flashlight is.
If being able to see in the dark without light ruins dungeon crawling, then dungeon crawling has been ruined for a very long time. But given the fact that there are myriad other ways to keep players "in the dark", so to speak, from mist, fog, smoke, illusions, hidden doors, fake walls, magical darkness, etc. etc., I don't really agree with this point of view.
Because even if you excised darkvision from the game, you couldn't just stop there. You'd also have to get rid of dancing lights, light, create campfire, produce flame, continual light, devil's sight*, polymorph and wild shape (into a beast that has darkvision), familiars, animal companions, any PC race that normally has darkvision when encountered as a foe, and a ton of things I haven't thought of yet.
*depending on whether or not you believe that this ability should include darkvision.