The thing is fricking white Helvetice Neue on a light blue bubble. You don´t need a retina display to conclude this is unreadable. You just need common sense.
Or just an opinion, which is what you have. It may be right, but until you have used it in anger, you must at least entertain the notion that it could very well be wrong.
Have you tried the current Gmail app? It uses thin fonts, and I don't find it to be a problem.