>>7027179Basically all the stats of the Combiner go up.
Shots that kill a normal Cybertronian just bounce off them when they're an arm or a leg. Strength, firepower, and so on. You're basically going from five guys with guns to a literal giant Superman.
The only problem is almost all Combiners are mentally unstable since the resulting personality is a combination of all the various impulses and thoughts which tend to be contradictory and emphasize whatever shared characteristics they have to an insane degree, but that almost never actually comes up in media. Technically only Victorion, Defensor, Magnaboss and Piranacon are without faults, although Piranacon doesn't really count since he's technically only one mind and six lobotomized retards. Defensor is united in their "protect all things" instinct, Magnaboss is ancient fucking Autobots that have been fighting so long they're of one mind anyway, and Victorion is a team of nuns with absolute faith in their mother superior which lets her do all the thinking for them.
Devastator, Computron, Superion, Predacus, Sky Reign, and Volcanicus manage to stay somewhat stable since their shared characteristic keeps them at least functional, but they're hindered either by stupidity, aggression, or inability to make a decision quickly enough.
Pretty much all the others, especially Thunder Mayhem, Abominus, Predaking, Bruticus, Optimus Maximus, and Menasor are batshit fucking insane and can literally only focus on killing something, which oftentimes includes their own side. Just raw berserkers you can barely reason with and just sort of point at the enemy. Its either because the personalities are too strong to blend together, or their shared impulses are all savage and aggressive.