I'm unhappy about Astarion's treatment too - he deserved better - but at least his ending is more satisfying than Karlach's. And Astarion basically brought everything on himself while Karlach was enslaved against her will. Just... ugh. Terrible.

One small sliver of positivity:

The House of Hope has a bunch of portals to various fun and interesting places. Hopefully Karlach can at least take a nice vacation from time to time.