That's a weird stance to take on a crossover fanfic where the main PoV character and most of the draw of this particular fic happens to be the Worm character.
Assumptions and how that makes an ass out of all involved aside, you'd be surprised at how many might not be familiar with her, but are purely Fate fans who don't really understand Taylor's story beyond what they learned here. So yes that was one of the reasons that no one really addressed when they took umbrage with my suggestions, which I specifically stated both of my recent posts in this thread were, and it's not like I didn't give a basic framework for a workable solution for James to use in the form of interludes from other perspectives.
But yeah the unexplained nature of Taylor's backstory is very much a weakness, narratively speaking. The Fate side gets more leeway because it started at the beginning of the story of Grand Order, but Taylor and Worm are in the exact opposite position given how this occurs Post-GM, and that prior story wasn't expanded on much in story, yet.
It isn't true that Taylor revealing it to everyone is necessary for the fic and would arguably harm it's quality because it would be out of character and not something Taylor would actually do as is.
My other more pertinent reason was the fact that EMIYA is probably internally freaking out and not in the mood for any more deflections or half truths regardless of Taylor's personality and trust issues; given how potentially dangerous Taylor is now given she just proved herself to be capable of controlling Phantasmal Beasts (which is something no modern Magecraft practitioner can accomplish so thoroughly like Taylor has given the inherent nature of such creatures if I remember correctly) with an unexplained power, the current situation where the rest of the team being unaware of the mechanics of her control and her history just became unacceptable. For someone like EMIYA, given his extremely cynical nature, him not learning how this is all possible would be extremely out of character.
Taylor might have his personal respect, but he's still a Counter Guardian who was summoned by a different person
without a catalyst. That doesn't happen without Alaya's approval. Even if he's in a Class Container at the moment, it's not unheard of for the Counter Force to summon Servants to resolve situations, since that happens in literally every Singularity and Lostbelt barring Fuyuki (and Chaldea arriving and being able to operate is likely still a Counter Force approved influence). Him being unaware of his purpose isn't a new thing for him it's probably happened thousands, maybe hundreds of thousands, of times in his past. Again that's not unprecedented, it occurs all the time for people acting on behalf of the Counter Force, knowingly or not.
This is
exactly the sort of situation EMIYA finds himself called upon for all the time by Alaya. Sure Taylor might be very against opening up, but frankly that's not exactly pertinent now. Even if EMIYA is biding his time at the moment, and that would be completely in character, theres plenty of potential opportunities for this event to occur in the very near future and he would jump at any opportunity, again perfectly in character. Unfortunately given Taylor's nature it'd be an extremely ugly confrontation that won't stay private for long, if at all, most likely, but that's just an opportunity for a clever writer to induce character development.
So yeah Taylor might not be willing to talk about it, but EMIYA wouldn't
care. This situation is already a clusterfuck of epic proportions, but Taylor's unwillingness to talk isn't something EMIYA would give a second thought of forcing if the situation demanded it, which it now is. Taylor was unaware she could control such creatures, EMIYA
just saw that, and that new capability just became a major liability. No one other than Taylor (and even she doesn't know for sure) is certain of how long it'll last, nor are they certain how effective it is. Does it have more strict range limits? Could there be growing resistance in controlled Phantasmals to the control itself? Given the nature of Phantasmal Beasts those are all
very likely possibilities. He's going to want details, no matter what.
Orders, Personality, Trust Issues, Rika's respect for Taylor, his respect for Taylor,
none of that will make a difference to Counter Guardian EMIYA. He's still Emiya Shirou at his core, he's just as stubborn as Taylor and this situation just shifted dramatically in this latest chapter. The Status Quo isn't acceptable in terms of team dynamics anymore.
But again these are just my personal suggestion and thoughts, potential issues that I foresee being a problem. James can ignore it if he wants to.