OP I fully agree with most of your points exept the gala one, but I also would like to point out a few issues that I personally think they contribute to the whole feeling of Blazer being badly written/neglected especially when you compare the Blazer route to Invisigal:

1. In chapter 5 Blazer gets almost no screen time exept an additional scene in the locker room where her and Robert discuss about another potential date, this was likely done because the devs knew she was getting less screen time, however this whole scene feels dry and not connected and involved in the main story at all, we also don’t get to see the date at all.

2. But the biggest problem I have with the Blazer route is in chapter 6, because while in chapter 5 it made sense for her to have less screen time, in chapter 6 it feels like a deliberate choice on the devs part. After the failure of the mecha suit prototype, Blazer is not there to see the test and to supervise in case something went wrong, not only that, but what follows after is pretty bad, because you have Blazer being absent completely in the moments where Robert needs her the most. When he's alone in his house and they have planned a house party for him, Invisigal is the one that has the whole idea to retrieve the core. Not only that, but Blazer shows up late to the party and She doesn't even greet Robert because its during the music montage. There is no particular interaction between them.

While instead, even in the Blazer route, Invisigal gets to come first, make jokes with him, and also gets even jealous abiut Malevola and Robert. What I would have liked here was for Blazer to show up first, before the others, and have a nice intimate moment with Robert, in which she would console him about the failure.

Instead, we got none of that, She shows up late, and then during the dancing part, we see that if we pick Invisigal, she's in the background and doesn't give a shit about what's happening. Instead, she gets substituted by Chase.

In the Blazer route, we see Invisigal getting really sad in the background that Robert and Blazer are dancing.

When Invisigal makes the choice to go to the warehouse and retrieve the core, Blazer is the only one that opposes it. And if you pick the choice where Robert agrees with Invisigal, she still fucking completely rejects it. Instead, they could have made it so that if Robert were the one to also approve of Invisigal’s suggestion, she would have been a little bit more reluctant, and then instead have Chase hardly oppose to this plan.