I definitely have a lower HR on inside z2 workouts than on outside z2 workouts.
What has been most surprising is how the shift to doing more z2 work has improved my 2-20 minute power bests. Here is a custom chart I made in WKO, showing all my power bests since starting structured training with TR in December 2017:
In Fall 2019 I did TR traditional base (MV), experimented briefly with polarized Nov/Dec 2019, and then Feb 2020 got frustrated with SSB and switched to FasCat SSB (more z2, less intervals). Then hired one of their coaches in August. I haven’t done any real interval work (sweet spot / threshold) since June - my off-season is June-August. The training distribution shows pyramidal and not polarized, averaging something around 8 hours/week.