The flaw is simple: you'll end up with only having as criminal defence attorneys those people who didn't succeed at being civil case attorneys, as everyone will prefer to earn more money with mostly the same training. So you won't have any outstanding criminal defence attorneys, which is equivalent to undermining the rights of those of need to defend themselves in criminal cases.
If you want to go this way, you have to go for the full-fledged solution: either the defendant choses their attorney (at a capped price) or an attorney shall be selected at random among all attorneys registered with the bar and must take charge of the case, the only exception being if they have a valid conflict of interest in that case.
But prosecutor salaries are (more or less) fixed, so if you let defence attorneys earn the same as prosecutors I don't think this harms the right of the defendant. You have a right to a reasonably good lawyer, but not to be defended by the most brilliant legal mind on earth who could get anybody acquited. The randomisation suggestion sounds good too.
A defense attorney is not defending only against a prosecutor in some kind of 1:1 coverage. They're defending against the prosecutor who also has a substantial fraction of the power of the entire government behind them. They can use a large amount of crime lab, detectives, investigators, etc.
If you want to go this way, you have to go for the full-fledged solution: either the defendant choses their attorney (at a capped price) or an attorney shall be selected at random among all attorneys registered with the bar and must take charge of the case, the only exception being if they have a valid conflict of interest in that case.