So let's say I have a problem (X) that needs to be solved. Most people in research use several approaches around a sub-topic Y. Most of these algorithms have performance of 80-95% accuracy so there is a space for improvement. I understand that a proper PhD topic would be to find a better solution here.
But what if I just use a new technique (K) to solve this problem? It hasn't been addressed yet in literature. I expect the performance of it to be lower or near the conventional methods. I justify using it because it's outperforming in imagery tasks and it would open up the literature to a new method.
If I use K to solve this problem and get lower performance than conventional solutions Y, does that count as a proper PhD thesis?
In other words, to define a PhD topic, should I find the problem to solve or use a tool and see how it solves a problem?