yeah that's unfortunate, because in many many ways it thrashes photoshop and even recently I've noticed adobe has started copying many of its features, but the alpha channel functionality baffles me. In photoshop I can just paste straight into the alpha channel, I can even just paint into it - this makes sense. I don't get how you do this in Affinity, if you even can its super un-intuitive, like i say this seems like basic paint software functionally to me, I don't see how Serif thinks its not an issue.
I wish I could tell everyone I know to buy Affinity, but it's incredibly hard to do simple things, and then by the same token some of its features are light years ahead of adobe - its a totally bizzare piece of software. Maybe in a few years it may be super good, but it just holds me up at the minute