Hey, everybody's entitled to their own opinions & preferences? Why wouldn't they be?
I've got at least my fair share of full-size, compact & subcompact pistols I can use for my instructor roles and as retirement CCW weapons. I tend to like smaller guns than larger guns for my daily activities, though. I spent enough years lugging around larger all-steel, alloy & then plastic "full-size" handguns.
I can't speak directly to the Shield, yet, since the LE models won't be out for a bit and I haven't been able to do any comparison work with one and my M&P 40c, SW999c, 3913, CS9, etc.
That said, I'd offer that a shorter barrel doesn't necessarily mean less inherent accuracy. It's the shooter & firearm interaction that create practical accuracy problems long before the machinery itself usually gets held responsible (sight radius differences often coming into play).
For example, my 3" CS9 can keep pace with my 3 1/2" 3913 all day long as far as practical, realized accuracy.
As far as concealment and the grip? Harder to call. Yes, grip
length can be an issue, as far as printing, and even comfort (pressed against and/or into the waist).
However, it's also the relative
thinness or thickness that can create an issue for many folks, and sometimes a longer, thin grip profile might actually work ... and feel ... better for lawful concealment. Just depends.
Capacity? Hey, you're talking to a guy who carried a 6-shot revolver as an issued & off-duty weapon for a number of years until they made me turn in my Magnum revolver and accept one of the latest & greatest hi-cap Wonder Nines. I carried (and still do, a 1911, too ... as well as one or another 5-shot J-frame. My CS9 uses 7-rd mags (as does my 4040PD) and my 3913 uses 8-rd mags. I'm not exactly losing sleep worrying about "capacity" issues.
Personal firearms selection is just that, though ... personal. As long as you're not restricted to something, suit yourself.
I'm cautiously optimistic that the Shield 9 will eventually (after I order one) influence me to retire my 3913 & CS9 to an even greater degree than at present.
Just different strokes.
I'm not putting away the J-frames for even smaller, easier to carry options, though.