I have to disagree, OP. I found my leveling experience to be the complete opposite. The 20s were tough for me, but once I actually went Immortal, and especially once I got Jaesa, things fell over dead. In my opinion, Strongs are way tougher than they should be (they have a much higher damage per second than Elites for example). However two of them are still always doable. If they're not, you need to check your level, check your spec, check your gear, and check your companion's gear. Keep in mind, quest rewards alone are *not* good enough to keep a companion's gear up to date past level 35 or so. If your complaint is about not being able to overcome the healing of two specific Strongs, then you had better not be using Quinn.
If you're properly specced Immortal and Jaesa/Vette are geared correctly, then you should be able to beat any solo quest encounter up to *at least* one level above you. Yes, that includes Elites and double Strongs. I've done it, repeatedly, so don't tell me it's impossible.