Darkholme
Performance Artist
I suspect the issue isn't with the fact that they managed to figure everyone out - it's the fact that you confirmed their guesses. Don't get me wrong - I believe that based on the IC information available to them, they should be allowed to formulate guesses and then have their guesses be confirmed to them. But as far as I can see, Team Assassin has only interacted with Lancer, Saber, Berserker, and notCaster. Based on that, the only people who revealed anything that could leave a hint to their identity were Lancer and Berserker(who I intentionally made easy to guess) - and Caster actually left behind a false flag, which would make it harder for them to make that guess ICly. As a GM, I wouldn't have revealed anything regarding any of the 5(7) other servants to a player unless they had earned it.Except I know the identities of all Servants and I can legit confirm Team Assassin have figured out everyone except for Ruler correctly with parameters, appearance pictures, and observing IC mannerisms alone.
I actually have to commend them for doing their best to win, since Assassin is usually seen as the weakest class.
Also you can stop with the arrogance. I am telling you right now they know everyone's identity. They actually gave me their analysis and reasons to conclude certain things. They figured out Saber because of Saber's Noble Phantasm parameter being A++ and matching accordingly with a certain other statistic that I can't talk about. Team Assassin is just the Magnificent Bastard trope being given form OOC.
Although, you do have a different, slightly more casual style. Even with me, you were willing to confirm one of my guesses in DMs. Normally I wouldn't mind that too much - clearly you have a lot of trust in your players. I think it was more Dal's comments about using that information to his advantage and "holding his cards close to his chest" was what caused the stir. That is basically a declaration of intent to metagame, which betrays that trust you put in your players.