The main problem is in 1v1 or 2v2 where you are focused mostly on base/engie management in the early game. You see a unit on your minimap. Was it a lab or a mantis? You couldn't zoom out and find the unit before it goes out of vision. Now you can't be sure what exactly you need to send to kill it.
I also don't really get the need for a whole new icon just for mantis, nor the argument that this destroys some of the uniqueness of the mantis. If it was unique it wouldn't function the exact same way as the 3 other mainline units which are all coincidentally tanks.
The uniqueness of it is covered by the fact it can help finish buildings with the 1 bp it has, not that it has a lab icon as a mainline tank.