I think I'm getting what you are saying, but, not 100% sure I follow. You are objecting to a creature having a continuous effect?
I guess that could be turned into an activated ability instead, "Target Creature loses all abilities and gains, "0: Until end of turn all creatures matching your mark gain +1/+1."
At least that way a mind flayer could neutralize it.
Not 100% sure I was following you though. I didn't get the mitosis part, how that related. (I do understand that you get the base creature from mitosis, just not sure how that relates).