Well, I don't dive with it, and I'm guessing 99% of us never get any of these 'dive' watches past 30m of water in the 1st place, so to me, the extreme depth capability etc.... is more illusion than capability.
That said, I love a meaty dive watch on the wrist, which despite my 1st sentence is why I kind of like the solid block (non-opening back) case. At least I can dream! "Yeah, if I took up diving, I'd take this baby with me". As a side benefit, I have to say the back of the 300MM hugs my wrist like few other watches. Maybe that's lug design (the Sumo also in nice in this area) rather than the presence or lack of a screw down back, but I know it works.
Re: the height, I could do with a slightly shorter watch, but then I also like the heft of it, and the 'extra' material to get that height contributes to the weight. Re: titanium, I'd rather it stay chunky. I've got numerous titanium watches, and while they're nice, I like to feel a watch on my wrist. I'll also confess to enjoying the reaction when people ask to see and, and their "Wow, that's heavy?!" upon having it placed in their hands. Is that a reason to keep it heavy, or buy a heavy watch? I hope not, but I'll admit to enjoying the look they give when they're surprised by the weight of it. Let's not kid ourselves, there's evidence to suggest that added weight is interpreted by many to be extra quality (Rolex, Rolls Royce, things like that)
I fully agree on the bezel, an insert (ceramic or otherwise) would be a big improvement. I bought a replacement bezel for my 300mm even though mine is perfect "just in case" as I expect to own this watch a really long time. I think sapphire would be a nice enhancement, and any redesign should play with dials, hands and surfacings on the case, but at the end of it all, I think (opinion alert!) if we are honest with ourselves, I think part of the allure of the 300MM is it on the way to being an 'homage' to its fore-bearers, it involves some compromises on the wrist.
If we made it with a back that opens, with bezel inserts, played around with the gasketing, changed out the dial, thinned it down, etc, etc..... next thing you know, we've got a cool new SKX007, and we've already got that (and I own/love them as well).