Having just spent a day doing some very tricky rotoscoping, I have been hugely impressed by how much easier it is with the new planar tracker in Fusion 9. It's genuinely shaved many hours off the job and made it a whole lot more fun, if you can say that about roto!
A lot of people think of a planar tracker as solely a tool for inserting screens or text into a background, but really that's only a small part of what makes it so useful.
If you have used the tracker in Resolve to track masks you will already know how this works. I don't know if the Fusion planar tracker is harnessing the same underlying technology but the results are just as awesome. It can really lock onto the trickiest of features and provide an automated solution that often needs only small amounts of manual tweaking.
I encourage you to try this if you haven't already - it's a game changer to have this now built into Fusion.
I made a short introductory tutorial about the planar tracker, but I only touched on how useful it is for more complex roto:
Make sure to use the Create Planar Transform option to maximise the value of this feature.