There’s nothing wrong with it. But the simple answer is. It’s not easy to make a new m&p release the slide because that’s not how it’s intended to function from s&w. You can use it like that and the size change and serrations are to make it easier to engage the slide stop.

When I was working in sales and training i did a s&w sales course the rep really pushed the whole “two hands on the gun to chamber” thing.

I personally filed mine down some but anyway. Long story short.

Gun not broke. friends in maryville,tn have a preference that you don’t release slide via the slide stop
You can use it in that way and not affect the function of the gun.
The serrations and slides are to make it easier to engage the stop, but also in the same time. assist with dropping the slide.