Bikewear in particular is a bit hilarious. I'm 5'9", 150lb, so a bit smaller than you, but I have significantly more muscle in my upper body than the typical serious cyclist build. In my experience, the more high-end the bike clothes, the more they expect you to be shaped like a TDF rider, which is to say literally zero upper body mass.

So I have almost the opposite problem from you, where an M is usually reasonable for me on the bottom, but _comically_ tight on top. Even an L is usually way too tight through the chest and biceps for me, but now not long enough in the arms.

I just live with it, because whatever, I don't mind the top being a little tight, but it is frustrating.