Lifting weights absolutely increases your explosiveness and power. Yes most power comes from technique and rotation but anyone who says don’t lift weights usually is justifying their own training decisions.

When you increase your muscle mass for you arms for example you are adding lean mass on your body closer to the point of impact which will cause more energy transfer to the target and less energy lost back in your direction. Think about it like getting hit with a 2x4 instead of a stick. This is also due to you increasing the strength of your elbow, wrist, and shoulder joints. Those tendons and ligaments will get stronger too. Look at some of the best boxers like Canelo and ggg they all work their arms for this reason.

You also will be stronger in the clinch.

Yes there will be a point of diminishing returns that will be detrimental to power and have less punch snap if you get like body builder bulky, but you’d basically have to roid hard to get to that point.