Re: possible reason we never seen the phaser rifle after w.n.m.h.g.b.
A pistol grip with a chamber that rests across the wrist is the most practical design for a human held hand weapon. Sci-fi productions have tried to deviate from it purely for the attempt to look different and modern... but it's still silly nonsense.
Well, Phaser I successfully accomplished that in 1966, and it proved to be as practical a hand-held weapon as the pistol version. Add the ability to conceal it in a way one cannot with PII, and PI could be the perfect Starfleet personal weapon.
"...to be like God, you have the power to make the world anything you want it to be."