I would argue that the issue isn't Tomoki being boring, sure he's not exactly fun or interesting, but that isn't in itself a problem.
I feel that the biggest issue is that when it was with Tomoko she basically deserved all the cringe and suffering, because she was an asshole and kept putting her foot in her mouth all the time, she deserved whatever happened to her and that was literally part of the comedy.
Tomoki though? He literally just want to be left in peace, he rarely ever is an asshole and when he is the person even deserves it, all he wants is to be left alone without any weirdo harassing him.
That happening once in a while was fine, but it has been happening so much lately that it makes me feel like "just leave the poor man alone".
I feel that's the biggest reason why Sachi and Yoshida being interested in him grates me, Komi something and the other girl being obsessed with him was established from the beginning, but why do Sachi and Yoshida even like him? He barely ever paid attention to them, you can't even argue he's a generic "nice" dense character, because you can literally see he's just respectful but doesn't give a single fuck about any of them.
It feels like this happened because the author literally have no other male character to use, Mako x Yoshida and Sachi x Minami are arguably infinitely more established than him with the girls to boot, so it feels kinda of forced.
I do admit adding a new male character would have been worse though, I give the author that, but the harem shenanigans are already getting stale.
TL;DR Tomoko harem is more interesting than Tomoki harem and I need a better hobby than ranting here
