I would change it to an on-gain trigger since Donald X. is moving from on-buy to on-gain.
Doesn't that just apply to cases where they are similar -- i.e., primarily to cases where a card just does something when it's bought/gained?
Here, the card cares about other cards being gained or bought, in which case it makes a large difference.
"Each other player gets +1 Worshipper" is almost strictly worse than "each other player may trash a card from their hand,"
I agree with the bigger point, but not with this part. You're using 'worse' as 'the bigger downside', i.e., 'the greater help for your opponent'. But trashing a card from your hand right now is often more useful than getting +1 Worshipper, and it may actually be more useful on average. Any draw-to-x effect, any 'discard your hand a and draw' effect, and menagerie would much rather trash immediately.