When I said common weapons (mid/short range) were a bad match against dynamos, I was thinking "like a Jr is a bad match against a .96". I mean, of course, if you lack range you need to work around. If you're saying "you can counter snipers", then it's the same for dynamos. There are several ways, and some were given here. I don't have a hard time against dynamos, or not more than against any other weapon. You just have to think about how to fight against each weapon.
Btw, lots of people have a bad timing against dynamo (myself included until recently). Basically, you are in stealth, you're waiting for the good timing to attack the dynamo: don't wait for the end of the flick. That's how you'll die or exchange with the next one, it's too late (unless you're in front of him, but you're not being that stealthy nor smart then). And that's not latency, I saw it in some videos too.
Dynamos are pitiful for long range weapons, more or less pitiful for half of the blasters, weak to any kind of bombs, and disrupting them is priceless. Add some moves, some stealth, some skills, and where is the problem? Sometimes I feel people are saying "I play the easiest weapon in the game, but this other weapon is really hard to take on, please nerf it so that I can still win without improving please". Or they are just sad because their easy-to-learn weapons (splattershot, .52, luna) are not that great against it. Oh, so sad. Would the long range weapons more played, everyone would possibly go "dynamo are bad, maybe make them faster?"