Your suggestion sounds like the strangler fig pattern. While a valuable strategy in some cases, it does present the risk of duplicating poor architecture choice

Your suggestion sounds like the strangler fig pattern. While a valuable strategy in some cases, it does present the risk of duplicating poor architecture choices into the new code. I would normally opt for your suggested approach too. However, based on the description given, I’d most likely recommend a complete rewrite in this case. The architecture appears to be quite poor and the risk of infecting new code with previous bad decision-making may be too great.