Just because it has a rail doesn’t mean hanging something off that rail will not have a detrimental effect on function.
It’s not a coincidence the FBI, which encourages WML on G19/G17s, prohibits hanging anything off 43x.
The overall length of the slide may be the same, but the recall spring assembly, which has significant effect in the timing window in the cycle of operation is not the same.
Glock 26’s work exceptionally well for a small-ish gun.
The slim Glocks are not the equal of the standard service sized Glocks (including the G26).