Hmm, I change the water in my 5 gal shrimp tank at the same time when I do my other main tanks.
About 50% once weekly is the usual routine for all tanks.
All 4 amanos and cherries all appear to none the worse for these water changes as far as I can tell. Unsure if actually had cherry losses in the past due to the water changes as doubt their bodies would be around for long with 4 greedy amanos and a bunch of snails
While it’s true shrimps don’t gave a large bio load, I think a weekly water change should be done to replenish minerals and fresh water. Even at 25% once weekly would still be ok imho but at every two weeks long term is pushing it but not unheard of.