Well, the more people are connected over p2p, the more potential errors could arise of course. But, I like to point to the game Factorio (
www.factorio.com ): The game runs p2p, sends only player control inputs over network, and simulates the running game (a factory) on every participating computer fully determined (e.g. there are no differences in what players see at every time). Now, the Factorio devs are writing such a clean code, that just recently, some youtubers built a factory with around 320 players (I think?) in the game at the same time, all p2p, no dedicated server. Somebody dropped or joined from time to time, but it didn't harm the flow of the game at all.
Of course this is Factorio and not For Honor, but I just want to show an example of how p2p works sometimes better than a dedicated server. If you take a look at the game, there's a LOT of stuff happening in a factory, and to send every position of every part to every player and still have a good multiplayer experience is simply impossible.
In For Honor, it's other reasons that speak for a p2p system. I used to link a good article from 2012 about fighting games mechanics, and why p2p is a good thing for it. If you're interested, I'll go look for it.
https://www.youtube.com/watch?v=nxmbb_NvFRo
Here is a Factorio video with over 200 players, can't find the 300+ right now. Please don't let yourself be fooled by the "simple" 2D graphics. There's a LOT happening under the hood, and a big factory not only looks very impressive, but brings even a high end PC to its knees for obvious reasons - you need to see, then you understand
And to the connection problems in For Honor: I'm not saying that the netcode works flawlessly, but I have a lot of games with people that seem to have their routers configured right, and we play 4on4 in the same setup for an hour no problems at all. Most connection issues I got is in Dominion and Elimination, and it seems to me that a lot of those are connected to red NAT (which can be changed easily if you got access to your router settings) or bad internet connections, like WLAN or a ****ty internet provider.
But, if it works flawlessly, like a few nights ago, I can play against a Chinese fellow who has to have at least a ping of 400-500ms to myself (I played with a buddy sitting in China regularly in the past, so I got some experience with the ping to there), and I can play the feint game with him without even noticing any lag issues. However Ubis Simulation works, it did very well in that case. With people from the US, to whom I got a 150-250ms ping, I don't even notice they are not living in my direct neighbourhood, so good are the connections.