Yes, FSI is still good.
https://www.youtube.com/watch?v=uEgFcImQ9XU Here you can see how often a higher level mob bashes. I have all the places in the video where a bash occurs marked in the description. I got hit 12 times by a bash on a 12ish minute fight, so average of 1 bash per minute. This is with a 75% slow applied.
For Shamans FSI is far superior to Troll Regen once you have Torpor.
For Warriors FSI is generally the better option. Most Warriors are not doing a lot of soloing. But Troll Regen is great if you prefer to solo on your Warrior.
For Shadowknights Troll Regen is is generally the better option, as Shadowknights are a great solo class, and many people use them as such. But FSI is good if you are someone who mostly/exclusively groups with your Shadowknight.