Design is not my thing as well. I code - mobile OSes, XMPP clients, backend/frontend, native utils, games, various stuff (majority of this as FLOSS contributions, even at work ;)) I was never trained in design, I don't care about it that much. Yet I see all those wrong paddings and wouldn't do them this way even in a quick proof of concept.

I don't blame the developers, I don't blame the project. I'm glad they do such client and would probably use it over the official Slack client even with its current UI (I'm more interested in a solid XMPP transport though). I just noticed that some people genuinely don't see or can't put their finger on those issues at all, which makes them unable to think about it and fix them without external help. And I wonder why it is like that - what makes you see those misaligned things as standing out, while others don't notice it?