it might be just me being dense but there are sus yoichi moments to actually back up the OFA's questionable morals thing??
It's not you being dense, most of it is me just looking at him and being <_<
But there are several things that makes him distrust him.
The first time First is seen in a memory, he explicitly says that meta powers should never be used for personal gains, which always disturbed me because 1. it's coming from someone who doesn't have a meta power 2. it's an attempt at telling people what they can do with their bodies and I am pretty sure the "quirks should be used only to help others" is what led to the anti quirk laws.
In the same scene, First tries to interrupt a deal between AFO and two people. One has a mutation quirk and is ostracized because of it so he wishes to be rid of it because of it while another was attacked by people with powers and wishes for strength so it never happens again. AFO switches them and in exchange, he expects them to back him up. While Yoichi is probably right to say that AFO is doing that only to gain followers... they are adults and the deal isn't unfair per see. To me, it always felt that Yoichi was opposed to it because his brother used his gift to gain powers instead of by altruism.
The memories he shows Izuku are from AFO's POV, which is sus in itself, but they are also carefully pieced together to show AFO at his worst. And I am not saying he isn't a bad guy but said memories showed that the situation was crazy and AFO brought some order. It feels like Yoichi was selling a white and black narrative because he didn't trust Izuku to perceive the nuances of the situation and to come to the conclusion that AFO is a villain on his own.
The fact that Yoichi spoke to Izuku in Jakku to warn him about Tomura is... strange as he had never showed this ability before.
During the whole meeting with all the vestiges, Yoichi tells Izuku this grand secret about how OFA kills everyone who has a quirk and how Izuku is the only one who can handle OFA, which always felt like bullshit to me. The reveal of the big secret that made All Might worried never made sense to me because All Might, who is quirkless and survived decades with OFA, shouldn't worry about Izuku, who is also quirkless. It feels like Yoichi telling Izuku that he is the Chosen One.
During said meeting, where the vestiges don't really want Izuku to save Tomura... First let the other talk and doesn't say what he thinks until Izuku shows conviction that he wants to rescue Shigaraki. Only then did he say that they had his back. Again, it feels like some tiny manipulation to make Izuku believe he is on his side and make him more receptive.
The dreamscape changed dramatically between Izuku's visits. They are inside a vault because it's the only thing that remains and two vestiges were guarding the door. Yoichi is hiding something.
Also, the quirk is haunted and copy and paste personalities, which is just sus.