It's not about the weight, but the composition of his weight...he still looks slight...I'd like to see him more involved after a year in the Rams weight training program.
Kupp's a big boy LA. For a wideout he's big, rangy, and most importantly he's got great pre-tackling instincts. Take a look at that pass he caught over the middle to set up TG's TD, he was fed right into the safety who came down to crush him but that body turn took all the inertia out of the hit. Part of that was his size too. One of the guys like Pharoah would have been crushed for certain there.
Stood pretty close to him during camp and he's all of 6'2" man. He's a lot like Todd Gurley, bigger than he looks in uniform.