I have to do my lettering at the thumbnail phase or I'll never leave enough room or be able to integrate it naturally. This is an issue I have struggled with all my life

Yes, I am the same. The lettering and word balloons can’t be an afterthought. I did a work for hire job a couple years back where I was just given a basic plot outline and someone else attempted to letter it after I’d done all the drawing, and it came out looking like crap