Hmm, I did the mid volume plans and went from San Pedro (4x8min with 5min rest) to Bartlett Peak (4x16 with 2min rest) and it wasn’t a problem. Similar situation to you, I’d been doing the Sweet Spot Base and Build plans for nearly eighteen months and wasn’t really seeing any progress. The Polarised plans gave me the required kick, with it being fine weather in the UK I did them all outdoors.
I did a full post on the plans in the experiences with PP thread - https://www.trainerroad.com/forum/t/my-experience-with-tr-pol-plans/56258/85.