I can't say that I've been playing four player chess recently, but teams only changed FFA. It did not ruin it. The only problem is the difficulty in detecting prearranged teaming. But unspoken diplomacy is not much of a problem. If you can't adjust to change, you might want to quit.
Teams ruin 4 way chess

No it did ruin it. FFA does not exist anymore at 1800s+. It is just more teams. Everyone always teams up with the player opposite them, just like in the teams mode. FFA means no teams, it is every man for himself. If sometimes there are these teams that arise than so be it, but not every single game everyone teams up always with the person opposite them...It is no longer FFA. I guess teams don't ruin FFA, they destroy it completely.

Players over 2000+ put their queens on the center of the board on their second move, then at move 3 they sac the queen for a pawn following with the other guy doing the same and you got and unstoppable doble queen check! Arrrrr I hate that, but I have also been reported several times for playing FFA and I don't like that either because I also collaborate some times, playing FFA it is so risky.
In 4 way chess not only is the teams mode a terrible idea and a terrible mode by itself, but it has ruined the other modes as well. In FFA now everyone (at least at relatively higher levels) teams up and it is exactly the same as simply playing the team mode. There is no point of even having FFA anymore. the teaming up completely ruins FFA, there is really no such thing as FFA anymore.