First, get out of the tank tree for leveling. The damage is horrendous in tank spec for Guardians, PT's and Assassins can pull it off. Because they have the dps in those trees, and aren't gimped by there resource.
And 2nd don't do pre-50 flashpoints, unless you are ready for pugs like you experienced. Not saying you wont still run into these types of players at 50, but they are few and far between.
Trust me when I say this, I have all 3 tanks class and I tank or have tanked with them all. assassins and powertechs are very much face roll when it comes to threat.
The only tank that has to work for threat is Guardian / Jugg, yes they can tank and keep threat. But they are the only tank class that has to jump through burning hoops.
And yes we have real time dps meters in this game.
I enjoy tanking on my Juggernaut & Guardian. It's old school where threat is earned via technique - not by competing with dps for damage aggro. Where taunts and aggro bombs are kept in reserve for emergencies & breakaways. I like the challenge of having to keep my toon's head on a constant swivel and having to use terrain features to break LOS & set up dps. I also like my tanking to be up close & personal, hence the preference for Jug & Guardian. Gimmie one taunt, one aggro bomb, one stun and one interrupt & I'll tank Godzilla with a whiffle bat and a frisbee.