I hear people make comments about agency too, but I have a hard time characterizing these effects as loss of agency. I certainly don't think being subject to a suggestion, charm, dominate, or fear effect would cause a character to lose any more agency than lying on the ground a 0 hit points would. They're all consequences of some sort of failure (or series of failures) in the characters' situation. And while they may be frustrating, they are part of the give and take of the fact that D&D remains a game and not everything goes a player's way all the time in a game.