OP - great question. I always wanted to ask the same question but don't really feel qualified to comment as I have never owned an Aimpoint. But maybe all you folks can both educate and sell me on this, because...
I have a Holsoun HS515GM and HS515CM. Yes, I know they are not Aimpoints but even on an elementary level, I don't see why something can improve on these because...
1. Between the dot and the circle reticle, it is easy on the eyes. Nice sharp dot/reticle. I have found it helps improve my really elementary shooting skills.
2. People say Aimpoints are reliable. Are these Holosuns not? My experience has been excellent.
3. Battery life is great. Rated for like 50,000 hours. My 515CM has solar power backup
4. Shake awake feature is awesome. I don't have to turn it on. And it turns off after 10 minutes (unlike my former Vortex at 12 hours)
5. My 515GM has glass flip covers, which I never flip since I can see right through
6. The 515GM is military grade housing. Dropped it, no issues
7. Everything is nice and crisp through the glass
8. The quick detach mount is very nice and handy.
Now I am certainly NOT saying mine is better than any Aimpoint...but never owning an Aimpoint, what would it have over what I quite enjoy in my Holosun and would be worth the extra money?
That being said, on my WK, I have a Sig Sauer Romeo 5, and it seems to do the job though not as many bells and whistles as the Holosun.