No worries, we all got plasma ***** by Warbirds at some point.
I tend to run away everytime the Intraku shows up. Since it decloaks right behind you, it has the clear advantage. So use all means necessary to escape out of range. Then start the fight on your terms. Attack from behind or the sides, try to stay at least 5km away (tractor range).
Having a hell of a time with this one too. I either get ***** at close range or I use my superior maneuverability to wear him down to 50% then he warps out and leaves the mission unfinishable. Does this kind of fight come up a lot? If so I don't know if sticking with STO is worth the frustration.
These Romulan mission are pretty tough at commander level. What I found out the other day was the fact that you get a lot of XP for doing patrol missions. Do some patrol missions, get to captain and then do these missions. You also have a bigger boat.