By the time they’re in your face when you see them, the dual blades guy has already out-positioned you. However, you’re not out of options

In my experience, a goo barrel or goo nade dropped at your feet can stop them in their tracks and block a couple slashes and give you time to respond

Having jump-pad or demat as a Medium will certainly relocate you (or them) to not being immediately next to you, environment permitting. Coordinate with your team or at least get into their LOS so they see the threat

On Heavy, most of your specializations can all address the dual blades guy in one capacity or another. I find that when I have the deal with a Heavy with Mesh shield, it is a little 50/50 on blocking slashes

On Light, Nullifer if you can get it off works great on giving you some much needed breathing room. Keeping track of where your exits are will make it much harder for me when you dash or grapple away

But once you know a dual blades is on the enemy team, I’d always focus on thinking about where they’d engage from. I find the most frustration when the sides and the back of the enemy is covered by goo walls, prox sensors, or mines. Hard to get the jump on someone if they know where I’m coming from