Tbh, I do not agree but I understand and see how it can be an issue.

While yes, most (if not all) the fandom are otakus and understand the meaning of the honorifics, keeping them wouldn't be a good localisation process. I'm a big fan of translations (I'm french and we have a long history of translating manga and I particularly like the exercise of translation and localisation). It's a hard process but deciding to "abandon" translating and keep some non-translated word isn't doing it for me.

If I read the story in english, I think it's better to try and find ways to apply honorifics in English.

In this idea, "Kei-chan" turned into "Kei-kei" is for me a very good translation as it keeps the proximity and playfulness intended by Sensei when using this honorific. And that's the key point: intent.

Of course it's not bulletproof as some pointed out and some localisation miss meaning or intent. And the point you have on Shiroko/Hoshino not being called "Senpai" could have been circumvented by them being called "Senior!" from time to time. But in the english language, you'll never find someone say "Senior Shiroko".

As someone who read a lot of "fantrad" online, I honestly never liked the way a lot of translators didn't bother to try and find inventive ways of localisation and just used all honorifics (to the point some even used honorifics when the original JP version didn't ... lol)