I mean, every weapon has its pros and cons and is balanced - there are some quirks and difficulties in handling the dynamo, in the same way that for example you need to be really good at targeting with the sniper weapons. Working around and adapting the negs gives you a very, very deadly weapon in your hands. I've only been rank B- so far because I didn't play ranked battle much, but so far dynamo roller gives a really good advantage for the actual objective.
I'm sorry I took the virtue of surprise from you, but I gave you the present of anticipation! The gold dynamo roller is absolutely worth unlocking if you're into the dynamo, the loadout complements it SO MUCH better than the standard dynamo. Keep up the grind!
Also, here's a tip for the movement while swinging problem: jump. Jumping before swinging lets you carry the momentum with you, and jumping mid-swing gives you a farther spread (good for covering turf) and makes you harder to hit for enemies. Practice what I affectionately call the rain dance! And if you have the gold roller, bombs can be advantagous in close encounters as they explode faster than you even swing.