New candidates can and do defeat incumbents all the time. Clearly, it is not an impossibility.
Meanwhile, saying "well this way that candidates could use to basically siphon money to themselves that isn't currently allowed totally wont be used as yet another form of funneling money in politics!" is far less reassuring, seeing as money and corporate influence in politics is already a gross problem.
Hell, if anything, it allows candidates who already have money and influence to spend more to drown out up and coming opponents because they can get that money back that much more easily. So not even the pretend benefit you supposedly support to veil the fact that you like that it puts money from corporate donors more directly into conservative pockets even holds up.