I think changing mercies is a bad idea because it makes faf even more mechanical. Mercies are a cheese mechanism, and a comeback mechanism much like tac missles. It offers alternative ways for games to take and therefore makes the game more exciting. Of course it sucks to be mercy sniped, or tml sniped, or old beetle sniped, or corsaired, but its a nice cheese thats super costly and all-inny. mercies have insane bt, so if you do your homework and scout and dont neglect air and radar and play zoomed out, they are super easy to counter.
Now i dont want to talk about mercies, but about the direction the balance has been going since im here. The game became more and more "be efficient in eco and grind down your opponent" style with less abilities to make plays, ie. Use units to conclude a game fast. If you remove mercies the games objective boils down more and more to "acquire mass to make t1 tanks to hold map"-style. Or in teamgames "be as greedy as possible and upgrade mex style", and i think thats boring. I like it when games have cheese options like fast ml that doesnt require half its mass worth of bp to be constructed within the relevant time window, or beetles to snipe acus, because thats exciting to do and punishes people who are lost in basebuilding and efficiency optimisation playstyle.