Trimming coatshort in summer?

My papillon (3yo male) loves being outside and loves going on walks. I live in Ohio so in winter his long coat works great and he bounds around in the snow like a husky.

But in summer he wants to run and go on 45 min walks still but gets way too hot (we get a lot of upper 80 degree and 90s). He pants too heavy for me to think its safe and sometimes he does turn around when he realizes he is too hot. Mostly he just is miserable being inside and grumpy without walking.

I want to get his coat trimmed or even shaved (with like 2in or so of fluff still) but I've tried 2 groomers and they've refused as "unethical".

Am I not supposed to get his hair cut for some reason? He definitely does seem to regulate heat well.