Thunderfire was a PITA against both my orks and my tyranids. Between no cover, making cover 3+, and creating movement issues, it sucked. Guy I play who uses it does a good job controlling the field with it. If the placement works, it has taken me till turn 3 or 4 just to get a shot off at it.The vindicator is a very blunt instrument. It's not bad, but everyone is 100% aware of what it can do and can act accordingly.
The thunderfire is much more subtle. It's shots can slow opposition units down (and potentially immobilise vehicles/prevent bike boosting), ignore cover or just cause a ton of st 6 hits. My tyranid army would be much more concerned about the thunderfire cannon than a vindicator.
Whirlwinds have had their day. A dakka pred is just plain better at killing light infantry.