well percentages is a percentage and thus if you are unlucky you can farm a place more than 10.000 times and still not get an arch priest.
1% chance is a chance calculated each time a priest spot is spawned.
so next time you slaughter to force new spawn, there is an 1% chance and so on and so forth.
but reason they changed the chance to 1% was that it was WAY to easy to farm, and potentially destroy weeks if not months of farming, grinding and building within a few hours due to high priests being “common” spawn.
therefore they changed them to be very ware due to them being so powerful - yes even after nerf. so imo its fine as is. as of right now, people don’t just use T3 alters, and arch priests every single raid pass, but save them up for that really powerfull enemy main base.