A really old topic but always valuable.
I work for french TV 1080 50interlaced. When i need to make a credit roll, the only tool i can use to avoid flickering is After effect. No tool in FCPX (even in Resolve) make the job in interlace.
So, have you find the champion ?
Best way to achieve a not jerky credit interlaced roll in FCPX is to make a 1080 50p project, render and export the basic FCPX credit roll and then import the result back into a 1080 50i project . The result is perfectly smooth on an interlaced control monitor.
Avid has the same problem, since the old Title tool disappeared (old but really good result for interlaced Rolling title).
We have tried Tiler+ with problems of regularity in rolling title, not smooth. We've also tried Boris FX Title Studio, with good results but as the same as the basic tool of FCPX, if we use th "french trick".