That is the problem. If you had simply applied a bit of rooting hormone and stuck it into the soil in the pot in the first place, or rooted it on sphagnum moss or dirty moss (sphag mixed with a bit of perlite and potting mix) it would have rooted more naturally and made roots that would be already acclimated to being 'planted' in mix.
Water roots are not that way. They are fragile roots that have never had to contact and grow through a substrate and 'toughen up', and they have never had to search our water through drier pockets of substrate where they would have been highly encouraged to branch a lot (thus making them make 'spoiled rotten' and now your plant will have to try and do all this with newer roots while it tried to support the leaves)
