While potentially replacing 18 validators at once could indeed be problematic, at the same time there is no need to keep the 95% level in this round of adjustment. I’d suggest raising it by 1% every 700 checkpoints until it reaches 98%.
On a separate note (maybe should be in its own thread)
A) I consider 98% too strict, the long term goal and single threshold should be 97.5% or even 97%. Out of the validators which are under 98% now, 43% (6) of them are between 98 and 97%. These 6 represent 7.5% of all the validators.
B) The network could come under attack and cause a lot of validators to fall below the threshold (be it 98 or 97%). Another unforeseen event could also have similar consequences. A limit on how many validators can be offboarded at once would be useful: for example, (completely off the top of my head), 4 validators per 700 blocks, offboarding them in order of performance (worst performance gets offboarded 1st) until all vals marked for offboarding are gone.