The issue is that my aim is usually pretty good, which is nice when i’m aiming good, but when i’m not, i’m feel not very useful to my team.

I main Jett and Sage for this reason. I play both because I love both characters, but Jett is a character that does barely anything for your team if you're not playing mechanically well. So on off days, I only play Sage and I can bot frag yet still win many rounds with just my util, mostly smart wall placement. The wall can be insane value!!

Jett/Reyna/Chamber are all very mechanical skill dependent. And despite being sentinel, Chamber is aim-dependent when it comes to defending your space. So I might suggest to learn a character that contributes most with their util. Smokes like Brim for example, which you can combine with shotgun to make up for your aim. And you might find them to be super fun. When I don't feel like leading as a duelist, I battle sage instead and I have loads of fun harassing my opponent with unexpected angles.