Enmity problems as a PLD.

[Synestr]

Flash isn't that bad to use on single target. If the blind sticks it helps with dmg mitigation and gives you time to Stoneskin or whatever.

I agree that FoF should not be used on your lob, it will waste active time. I use the following and have only rare occasions where I lose threat.

Lob > Flash (as I run through the mob) > FB > FoF > SB > CoS > RoH > FB > SW > SB > RoH > Bash (SWIPE if it's up) > Flash, this allows you to get the most benefit from your 20s of FoF. From here you can just 123 using CoS and SW when they are up, flash when you want, SS etc.

I think what may be happening in your rotation that you posted is that you front load a couple of moves that aren't boosting your enmity -

...I usually start out a boss pull with something like Fight or Flight -> Shield Lob -> Circle of Scorn -> Fast Blade -> Flash...

Most DPS are trying to smash that boss from the get go, with a ramp up of 2 or 3 OGCD (BFB, IR, RS), with this being the case they are generating threat in their opening that you are with yours. By the time you get to your flash, you are just starting to catch up. Make a slight adjustment and you should be ahead in threat.

This is the opener i use aswell due said double scron under FoF buff, there is like 2secs or so left in FoF when scorn comes from cooldown.

Though I agree that it's nice to get in two CoS under FoF, but for ST as the OP is concerned with, I don't see the benefit. Sure the DoT is cool but you would be better served to ensure you get more of your threat combo in during the up time of FoF. NOW for larger pulls, yes, FoF before CoS is a good idea. Better AoE generation and a little DPS are always welcome.

Hope my advice helps!