considering ive beaten the whole game with this method? most of the time doing so on my first try at a stage? yeah pretty sure.
example, first stage the ranged guy is the green slingshot looking one. just pump into range, send them in the middle since that has the enemy closest to spawn (golden pot thing) and hitting an enemy generates xp, so you want to start hitting him asap. 5 or so upgrades into range should be enough that you can attack him without being attacked.
farm exp, get the range high enough to outrange all the plants, and have enough capacity to send at least one slingshot on each row.
also several enemies have piercing shots, that trivializes the stage since one piercing shot can hit the rope even if the enemies are there.
also if you didnt notice the enemies you fight are your units in the next stage, so keep an eye on what they do/what their attacks are so you know which one to use next round.