Why am I so physically weak for my size?

You’re shorter in the evening?
Practice practice practice. If you don’t use those muscles they will be weaker. The more you use them the stronger they’ll be.

Bench pressing 275 is weak?

I’d love to be able to bench 275. Conversely, I can curl 120 lbs, and am 5’10” and 170 lbs. We each have unique strengths and weaknesses, but we’re all able to improve on our strengths through continual exercise.

You’re probably not working out your chest as much as you do your arms. Do chest presses to target your pectoral area.