I don't agree on your about giving too many things dissociated from the mc's feelings. By occasionally following different characters, often for flashbacks, the game is employing a solid storytelling device used in many great novels. It's put to good use here for "showing" some of the character's backstories rather than only "telling" them. The most moving part of the game is of course Emma's backstory, told mostly from her perspective. Sure, by expanding the scope of the narration beyond only following the mc, it creates a disconnect between the mc's knowledge and the player's knowledge, but this is commonplace in video games. It's really just a different style of storytelling to that which creates a one-to-one link between character and player knowledge: neither is inherently better or worse.
.I'm talking about literally not having any reason to side with the mc's bottled anger and frustration. We see what Gwen, Aine and Emma are like before we see what they did to the mc. We get presented reasons to think mc is taking things too hard because we only got meh examples of how they bullied him. We get to know that the mc kept following Aine around when she was bullying him by his own choice cus he was simping too early.
Basically we don't get to sympathise with the mc for getting bullied. My main focus of the rant is how we get to dismay mc's feelings of unease and frustration with ease.
Also the scenes of the other characters without mc tell us too much. Not enough left for speculation. We get to know everyone's personality.
Also Jess reveals her relation to Hera too soon after Hera's reveal. Also Hera gives you the motive literally on her debut.
Personally, I was able to empathise with the mc's experience of bullying despite the points you detailed, but I do understand that it would have been more impactful to have been shown some of the scenes rather than them being described in the abstract. That could have clarified his relationship with Aine while in school, because as is, it isn't entirely clear why he stuck with them. Simping just isn't a realistic reason. So yes, we are left wondering whether there was a good reason, or whether he is complaining over nothing.
I still personally like the scenes which delve into the detail of a character's backstory, revealing a lot about their personality and how it formed. Some games choose to trickle every character's story out over a long course of time (this is done very well in Harem Hotel). However, I like the way this game occasionally chooses to dole out large chunks at a time. Emma's chapter made the most of this, delivering a very moving and self-contained mini story, which wouldn't be the same if it was spread across multiple chapters. The developer has also decided to take a more measured pace with some characters, such as the pizza worker / runner (I forget her name), and these also clicked with me.
Nevertheless, I agree that the pacing isn't always perfect, and Jess' reveal is an example of this. I imagine pacing is very hard to get right given the serialised development cycle of these visual novels. Fifty Shades of Grey is an (extreme) example of how serialised writing can result in a meandering mess (in case you didn't know, it was originally written chapter-by-chapter as a Twilight fan fiction). I think My Bully does an admirable job of threading the needle.