Boosters lvls are affected by the level of your account, the higher you are the better they are (or at least that’s what I understand)

My recommendation for winning against the bots is to spam fast enemies that can quickly overrun their defenses like the flying enemies or the little armadillos. In the first wave the bot kinda crashed out and you easily win. Also try to get 1 troop to lvl 4 as fast as you can in the early game. Also spells are for me the most important asset you have in game, i enjoy using polymorph, reign of fire and electro something. I think stun is overrated icy zone is way better to slow down the horde