I’ve had 3 Golfs and kept each one 4-5 years, so have put each one through at least one MOT and none of them had an extended warranty (so running without warranty for up to two years). They all passed each MOT with no advisories, and none of them required a visit to the dealer for anything other than servicing/MOT in the fourth year of ownership.
I know there’s no guarantee that a car will be problem free once it reaches 3 years old and many owners wouldn’t want to run a car without it having benefit of the manufacturers warranty, but in the OP’s position, I think I would’ve extended the lease for a few months on the GTD and ordered the R for a March 2019 delivery.