In my experience the alerts are very hard to miss, but I can understand your point.
I find the Shearwater method for alerts works well. The top 2 rows on a Perdix screen are considered "critical dive info" and they are always displayed, no matter what - unless you explicitly flip to another screen, like the compass. The bottom row is additional info that is not considered "critical".
For alerts (e.g. dropping below tank pressure Reserve setting), they display replacing the bottom row of info. Usually in a different color. The user has to press a button to dismiss the alert.
Now that you mention it, lockouts are configurable to an extent, and enabled by default. it is up to the end user to disable if desired.
I did not consider editing GF or mix settings under water, so I can't comment on that ability. When in dive mode the watch is locked to a specific subset of screens. As such, my gut feel is that the initial answer is no.
The one other thing I have noticed over the years is that Garmin is a company that values customer input. I'd never count anything out if the market demands specific features.
I looked on the Garmin site and the User Manual appears to not be available yet. I will look forward to learning what the details are on lockouts and configuration.
Lockouts and changing GF settings during a dive kind of go together in my mind.
Let's say I start a dive with GF50/80 on my Perdix. Stuff happens during the dive and I now need to get to the surface as fast as I possibly can do so somewhat safely (i.e. not just blow and go). I start my ascent immediately, which registers as skipping a mandatory deco stop. As I'm ascending, I go into my settings and change my GF to 95/95, so that it still guides me through a very aggressive but still somewhat safe ascent. With the new settings, the deco stop that was originally called for completely goes away.
The fact that I initially "skipped" a mandatory deco obligation should not cause my computer to lock me into gauge mode after the dive is over. Especially in a scenario like this where the deco stop went away after I changed my GF settings.
Alternatively, a different scenario: I start a dive with my GF set to 30/50 because I was experimenting with my computer the last time I used it and I forgot to change it back to my "normal" settings. I get down to the bottom, check my computer and notice that it's got me going into deco a lot sooner than I should be. I realize what's up and change my GF settings to my "normal" settings and carry on with my dive. At that point, the computer works the same way as if I had started the dive with my normal settings in the first place.
And if I got locked out simply because I started the dive with the wrong GF settings (but completed my dive as planned - presumably based on a backup computer and/or wet notes), that would be totally unacceptable. And especially if I could not change the settings during the dive.
If I could not do those things with the Descent, that would definitely dampen my interest in one.