A few things you won't have done in a plank:
Confined areas, take off/land on sloping ground, limited power operation, quick stops, hovering in/out of ground effect, engine off landings (OK, you've done glide approaches, but a full auto is a tad different).
The RN put all RW studes through 80 hours on the Bulldog in my day (now it's 60 hours), just to teach them airmanship, LL nav etc., and the syllabus planned for first solo at 12 hours in the Gazelle, arguably a much easier platform than an R22.