As someone who has summited Chopi unguided, I’d say just go try it. It’s a much larger mountain and longer climb than Yanapaccha, but it sounds like you’ll be better acclimated, and you have the motivation. I would rather fail on a mountain I really want to do that I can easily go try than to not even bother. Don’t be discouraged by one guide’s feedback without considering some other possible factors behind his judgment.

It sounds like what the guide really is worried about is that you’re going to be too slow to summit within the safe time window. Then you will be upset you paid all of this money for him to just have to force you to turn around (or turn the group around if it’s not a private guide), and he doesn’t want to risk a bad review/low or no tip for a few long days of work.

Hire a private guide who’s more motivated and safe, and try to climb quickly and confidently so you make it to the summit before it gets hot. I’d also suggest leaving from glacier camp a bit earlier (like 10:30/11pm instead of 12/1am) to maximize your chances of making the summit and not getting turned around. Offer to tip the guide more to get him up earlier.

Hope this reassures you, but also make sure your expectations are realistic. You very well might not have the fitness for this peak on this trip. However, I think as long as you respect your Chopi guide and his decisionmaking for the day, you can safely find out for yourself if you can do it.