Out of curiosity, what problems would mainly be precipitated from "overleveling" a Pokemon? What drawbacks could happen from leveling up a Pokemon too much beyond a certain point?
My supposition is that it may be evolution-related, but the term "overleveling" is a bit abstract if it is not entirely clear where the delimited boundary of overleveling is; if the problems of overleveling are not clear either, it's not entirely clear to delineate where the boundaries may lie.
I'm not trying to insinuatively suggest that your solution is not the most sensible one; I'm just looking to identify the underlying problem behind this. Once the underlying problem is successfully identified, then other viable alternatives can be devised.