Well - that's true apart from co-incidence. You can have a very simple theory which says "x is directly caused by y" and there is a lot of good data, and a great fit. But it's kist a co-incidence and breaks down immediately.

Occam's razor is a rule of thumb and an aesthetic boon, but nothing more.

The real test is that you have a theory that is meaningful and has explanatory power. If it grants insight on the mechanisms that are driving the relationships or generating the data and these make sense - you are pretty golden.

Another one is that the theory makes unexpected predictions that you can then test. This is a real winner, and why complex physics is so well regarded.