Can I ask a question? When you say Horizon is the "strongest legend in the game" - do you mean it? Or do you simply mean she has the highest encounter win rate.
Because, not a single professional apex player would say horizon is the strongest player in the game. Not a single one.
However, good players gravitate towards Horizon for her mobility, since you turned pathfinder into a walking fridge. Do you not equate for this in terms of what legend is "strongest"? Pathfinder no doubt used to be the "strongest" or one of them, but you nerfed the grapple and hitbox so now better players are moving to other characters.
Wattson for example is evidently only played by a small amount of people. I would wager the majority of Wattson players are highly skilled players still playing Wattson from a time when she was firmly in the competitive meta (she is not anymore).
Therefore, your average Wattson player is probably of a much higher skill than your average Mirag...