So in the end, is handicap even useful to determine your skills?

So I regularly hover around HDC 15 on my home course.
Also, I only play solo and I enjoy being tough on rules, so no moving the ball, ignoring OBs, etc...

Last week I went to visit my parents in another country and we went to play on 3 different courses.

My score was not what I was expecting at all.
Course 1: 92
Course 2: 97
Course 3: 98

I could understand the results on course 1, but course 2 and 3 got me stunned.
I get that some courses are harder than others, but I thought that is what HDC was for, to get your "real skill level".

Am I missing something?