There are some things to consider:
Prevalance of condition immunity
Stunned has quite a few monsters immune. Incapacitated has none. That initially makes monsters immune to the condition that normally wouldn't be.
No means of ending the incapacitated condition
There are some (very limited!) means of ending Stunned
Makes things more dangerous
The incapacitated condition can be delivered via a lot of other means and conditions. Wrapping that into stunned adds additional negatives besides action restrictions.
Giving attacks advantage and autofailing strength or dex saves increases damage/death risk. You have also removed movement as an option by moving to Stunned.
This sounds like what you're going for, but thought I'd spell it out :)
