This is Eri giving dating a go.
You need to actually understand the reasoning behind Eri "giving dating a go". Is it because she actually wants to become Fuyuki's lover? Is it because she's not quite there yet, but believes that she'll come to love Fuyuki as a girlfriend given enough time?
No, it's because she's not willing to give Fuyuki the time and space she needs to move on and heal so they can be friends again, so she launched herself at the opportunity of being Fuyuki's "one and only", even admitting that she will most likely never return her feelings and just end up hurting her again in the future.
That's her solution to seeing her break down over an unrequited love. Dangling a carrot on a stick in front of her eyes, because she cares more about herself than she ever did about her treasured friend. For Eri it's more important to keep Fuyuki by her side than allowing her to move on from the love that made her suffer for years. She will not accept anything else because she simply can't let go.
There is no reasonable argument based on "it's because her feelings are evolving", "it's because she's trying to understand herself" or similar, when the story already clearly showed what Eri thinks and how she feels. She's selfish and greedy (she says so herself) and that's why she did all of this.
Underneath your position (and those who argued against Shiho/Aki's future) is I think a fundamental misunderstanding of these characteristics and a desire to see them as something set in stone
I'm not stranger to these kind of relationships and stories. Sasakoi handled it very well, because there were basically no stakes and it happened after all the conflicts between the two characters were already resolved. Aki didn't
need to date Shiho, she just wanted to. Eri doesn't want to, but she needs to.
There is no point of comparison between the two couples, you're talking about completely different stories. That's why the arguments that we agree are stupid when applied to Aki turn out to be valid when applied to Eri. Just because the argument is roughly the same it doesn't mean it's always wrong. Come on.
as long as both women are mutually aware of their decision there's nothing wrong regardless
Saying there's nothing wrong as long as both parties agree is very naive. One of them isn't in a position to think clearly.
She even tried to say no, twice. But Eri doubled down and convinced her. Again, it comes down to consideration. If Eri really cared, she would do what's best for Fuyuki; instead, she decided to go on the offensive and talk her into dating until she agreed. She's been in love for so many years, how could she reject such an opportunity when her beloved is insisting?
But Eri could never have that kind of consideration. She isn't willing to sacrifice her own desire for her friend's sake.
For the record, I do think Shinoa's intention was writing what you describe. But be it because she only has so many chapters to work with and couldn't fit enough screentime for Eri while focusing too much on Fuyuki or some other reason, that's not what comes across in the actual story.
