I can only answer for myself, and to a degree, what I see my LE colleagues doing. I have carried a shotgun at work since 1984, night shift big-city police patrol, with a brief interruption in 2002/2003, when I carried a patrol rifle, and allowed myself to be persuaded to sell my shotgun. I agree that the AR15 gets more attention these days, but the shotgun remains a visible presence, especially among officers who have not yet attended one of the too-rare 40-hour certification classes.
I bought an 870P soon after realizing my error in selling my prior shotgun, and for a while, had both shotgun and AR15 with me, on patrol. As my eyesight diminished, and my aging, gimpy right knee rebelled against the timed, athletic patrol rifle Qual, I elected to let my AR15 certification lapse, and sold my Colt Govt Carbine to a younger officer. I still have that 870P, and just bought another.
I have no argument with those who prefer an AR15, or equivalent carbine, for self/home-defense. Their reasons for preferring the defensive rifle/carbine are valid. I am quite comfortable with the shotgun, and the real-world, local results of buckshot pellets stopping felons, from time to time, validate with my comfort level with my choice of weapon and ammo. (I keep slugs around, too.)
I would, almost certainly, prefer a rifle for police patrol if I worked during daylight hours. (That would be unlikely, as our nearly-black, dark navy blue uniforms become instant-bake ovens under the harsh Texas sun, and I am less heat-tolerant than during my younger days.) At night, an 870P is comforting enough.
Off the clock, there are times and environments that favor one or more of our rifles. Most of the time, however, especially at home, an 870P is my comfort gun.
I am not trying to persuade or convert anyone. This is what works for me.
Be safe and well, and have a good day!