Is thier significant rewards lockex behind it or just epeen stroking?
Significant rewards unfortunately
Technically true, but rewards are not locked behind progress or scores. The words you're posted so far are implying that you have to play endless and get really far in order to get good shit when this isnt true.
While class balance is slanted towards particular builds, that has nothing to do with the drops. I farmed endless for drops a lot, but I never even bothered with attempting a single lap and I still got tons of good drops from reaching a certain point (in a casual manner mind you) and leaving my desk to do something else and let the timer run out.
The high score aspect of endless is a community challenge oriented thing. The only objective rewards you get from reaching score milestones is titles and the rewards from titles, which is just a small chunk of SG (think around 200ish). Not only that, but regardless of your class choice, as long as you're in a party you can still make it far and rewards are also not based off of party comp, so 4 man and solo get the same rewards.
Of course, you're more likely to get more stuff the longer you play in a single run but that's by virtue of fighting more shit that has drops. So if you want to farm efficiently, then yeah it'll help to be able to run 1 lap to technically fight everything that drops what you want.
Deadass tho bro? It aint that deep. It's non essential content for anyone not aiming to live in end-game or engage in community driven score attacks. Sega has never held an endless oriented event and has always been treated as a side thing at best.
While the endless quest complaints will likely come, make sure that when you make threads like this that your a bastion of good discussion.