While I do agree there's a problem here, specifically the clutter caused by zoan abilities, I don't think repurposing unrelated abilities like that is any better, for gomu it is done specifically because they're sort of "evolutions" so it makes sense, but doing stuff like this adds a lot of complexity for the ability code and for maintaining it over the years.
For transformations they can be merged as they are related and it makes sense, however my biggest problem there becomes usability, as suddenly you need to make sure you're on the correct type before transforming which might be annoying to keep track of, where as the current way allows you to just press the button and you know 100% thats what you want without having to check if its the correct mode or whatever.