On-topic: I agree with the OP, but probably for different reasons. I agree because I main a rogue and playing Sub 24/7 as the most viable spec becomes boring after so long. Sometimes I want to go mess around with Assassination because DoT/Rotting specs are fun, but I don't feel like playing a caster (Lock/SPriest/Boomkin) and DK's are too tunnel-visioned. However, Assassination is heavily thwarted now because it lacks an MS effect and running WP as Assassination is a MASSIVE damage cut, but not having an MS effect running means the enemy healer is having an easy game, easy life AFK healing through your damage. It would be nice if they brought back the passive talent effect Assassination had where you could get the MS effect from Deadly Poison and make it a passive ability now.
Assassination benefits from sustained damage and a bit of burst. Combat is just... It's just not fun, at all. Sub has extra utility, but it's so bursty in ShD that utility almost doesn't matter now. Sub is more about tunneling damage now than it ever was, which is sad, since the spec should have remained about decent burst and strong control.
I'm speaking about rogues because I main a rogue, but I'm sure this affects other specs as well. The only specs I don't want to see in arenas being viable are tank specs because when they're good, they're TOO good (never die, take almost no damage, do too much damage, some can self-heal far too much, i.e. Blood DK's).