Of all of the things to complain about for the campaign, this is a bit of an odd one. Chances are if you actually made it to 500, you should have a team that works at 500. Not only that, nothing says you have to clear every room, so pick a faction with 3 rooms and just rush to the exit.
Actually, they probably think the average person hasn’t finished every delve to 500 and wants them to naturally play their 3 delves a day to progress upwards. 60 is still a really low bar. The faction assault is just a convenient secondary option to allow low level play.
If you think its bad now at 60, the requirement is only going to get higher later in the campaign.
It could have been worse, like requiring it to be done in a specific delve or even at a way higher delve level, like 200+