Most versions of Mitosis makes FGs easy. For instance: Mitosis scarabs. Tons of HP, eats ev erything, gets lots of damage due to it.
Umm...this is just a patently ridiculous statement. For Mitosis Scarabs to work, the Scarab with Mitosis has to stay in play and unmolested -- as do all of its spawn -- for X+1 turns, where X is the HP of the FG's creatures that you want to Devour.
Go check the number of FGs that don't have any creature control (which kills this deck outright), and then check how many of the remainder will outrush you EASILY within X turns. I guarantee you the total is 100% of the FGs -- ALL of them beat Scarab Mitosis.
And that, at heart, is the problem with all of these arguments against Mitosis: none of them take into account what is ACTUALLY required to make Mitosis work.
Mitosis is WEAKER than Fractal in every single way except one: Mitosis can, if the enemy has no CC, eventually create more of a given creature than Fractal can. It's slow to create creatures, it sits on the board where everything from Rewind to Psionic Wave can make it go away, and it takes away the skill of the creature you play it on.
The arguments against Mitosis are strictly born of ignorance, with one exception: Mitosis on a flying weapon does remove the card disadvantage inherent in creating more flying weapons, and that is, from a mechanical point of view, actually overpowered in a literal sense. Removing the ability to target flying weapons fixes that, and nothing else needs to be done to it.
Restore the original casting cost, remove targeting weapons. End of story.