Otherwise its endless kiting and kinda defeats the purpose of rocket bots are being anti structures. Currently rocket bots are anti-everything and thugs or maces only has unique use cases such as killing coms in 1v1 or ffa. At early game pawns and grunts becomes non viable very early so t1 fights become "who will make more rockos faster" . Rocket bots also counter all kinds on vehicles on t1 so its nearly impossible to counter them without mass spam or t2 units. Making thugs and maces faster than them will create a push with thugs/maces kill towers with rocket bots kinda dynamic which in my opinion would be more natural for the game.
This problem can be clearly seen on Supreme Isthmus front (everyone plays rocket bots like no other t1 units exist in the game) and other maps consisting narrower fronts. These 2 types of units should be more situational like mace/thug for pushing rocko for defending/killing structures/countering vehicles. A little speed tweak can fix this dynamic so chasing rocket bots with plasma bots can be viable and we would get more intense and fun t1 fights in the game. It can be like 40 speed for rocket bots 45 for plasma ones so it would not be easy to catch up to rocket bots but could act as a strategical decision.