I just don't get the use case of a sword that can turn into an animal. Might be useful for someone who hasn't high potency as a swordsman in the first place, but Zoro turning his swords that can decimate any opponent into a dog, what the heck is that good for.
That is because you are overlooking or dismissing one aspect of power - combat style.
The use cases that you mentioned are certainly as you described, useful for certain people but of no use to Zoro himself.
That is because Zoro himself is a collection of the best possible abilities.
However, for a guy like Shiryu whose job is to fight the best of the best, that will certainly be useful.
And it will compete with Zoro in one thing where Zoro is best at - combat style.
That is why I always give credit to Kaku, as the only guy in the whole show who has managed to pressure Santoryu.