is jerome overpowered?... to put it simply - no.I'm kind of noobie in RTS but i feel that if Isabel could ghost in the machine the hijacked vehicles , these Isabel vs Jerome matches might be more balanced.
is isabel underpowered?... debatable.
what can you do as isabel to stop jerome?... not much. you have to play irregularly to make it to end game because throughout the early game you're going to be weaker than he is. neither of you have any sort of early game economy, but jerome has inspire and time for heroes. because of that it's just a poor match up. isabel's late game can be decent because you get to make vehicles quicker, but jerome can hijack 3 of those vehicles. spartan vehicles cant be ghost in the machined either. if you can build your army up bigger than his though and then mac blast his heroes into extinction you'll have a chance.
isabels decoy and heavy metal arent very effective as opening powers. then you have turret drop and restoration drones which are wastes of resources early game. mac blast is the first power you get that actually matters and accelerated assembly is a great passive, but because it's a tech 2 passive that you wont get until your 3rd point it comes a bit late. lotus mines are generally considered useless by a majority of the player base though i like them somtimes. the best offense requires you to build specifically nightingales and/or scorpions. combat salvage only works on vehicles further forcing you into a specific army build. ghost in the machine requires your opponents to be using non-hero occupied vehicles and have those vehicles in a specific clump so that you can either have those units destroy themselves or destroy the other army and be in position for a mac blast.
isabel is a great leader, but her powers just dont do anything for her. i could see isabel having her leader powers re-positioned to grant her an earlier mac blast or lotus mine. or replacing her heavy metal, turret drop, or lotus mine with something more specific to her and her part in the campaign. even going so far as to allow her to self destruct the units she steals with ghost in the machine could help provide her with play maker potential. due to her not having any unique units it's hard for her to face opponents that do.