The rate of getting 90 IV mon from raid??

Stats are 10~15 each for egg hatch and raid catch. \
The random part is unbiased - ie, it's 9+1d6. The total stats is 27+3d6. There are 216 combinations. >90% means 4 or fewer points below max. There are 35 ways to get that with 3d6, so just under a 1/6 chance of getting >90% IVs.

I feel like my raid catches have generally been better than my egg hatches, but it's probably pure luck.

It's the same as egg hatch distribution:
https://pokemongo.gamepress.gg/egg-iv-distribution
So the answer to your question is 16.2%.

50 % 2 lapras raid!
Got this and the other one was less than 80 % IV.