I was able to port over my Airmail action from Drafts 4 to Drafts 5 easy peasy.
Sending to Drafts from Airmail is something that the Airmail devs still need to fix. They’ve been busy developing new apps like Cappuccino and Strike. That said, I’ve experienced some problems with sending to Drafts from the share sheet as I highlighted here. Obviously that’s not the same as AIrmail changing their action, but it might help alleviate it somewhat.