Many people hate to see old content nerfed. The truth of the matter is; old content needs to be nerfed to allow newcomers and the less skilled to catch-up. This does not mean that everyone can't be happy.
Solution: SE - Make a new achievement / Duty Finder category called "Time Capsule." Start putting some of the "big" historic battles on the duty finder under settings where your stats are capped to the original conditions (EX: Twintania - Item level 91, no echo, level 50). This would be incredibly easy for SE to implement (easier than savage coils where they are actually changing the battle conditions). Reward achievements and mounts for completing "Time Capsule" battles.
This isn't me trying to be a snowflake (in fact - I've never even attempted Twintania). This is purely a mechanism to keep challenges and goals alive for the lifespan of the game and there is literally no good reason for anybody to be against this (I can only think of selfish reasons).
In 5 years - try to find 8 people who just for the heck of it would cap themselves at level 50 (I-level 91), not use echo and try to take down Twintania. Provide an achievement incentive - and you'll have a much better chance of finding people. This does nothing but good. It allows newcomers to experience old challenges and it allows people to return to old battles under their original conditions for nostalgic purposes (it also creates more goals and things to do for all players).
This is what SE should do to differentiate itself from other MMOs. Like other MMOs, SE is implementing vertical progression and steadily releasing new content. This doesn't mean the old content needs to be "nerfed" for "everybody." Many would love to revisit fights they never had a chance to complete (or even those that they did complete). The pros most definitely outweigh the cons.