Yeah FTP building is actually a funny idea. This is what is popular these days but what is FTP? It’s just a test. You want a plan to increase your ability to do ramp tests? I am being “funny” but pointing out the problem that other good coaches have idendified. Everyone wants to build their FTP but really you should focus on building your ability to meet your end goal. Faster at 60 minute efforts? Faster at longer efforts? Preparing for a race. Just improving your FTP does not necessarily mean you are better prepared for your goal. TrainerRoad pushes sweet spot because it does build your FTP rather quickly but the problem is that is a short term strategy. If you want a long term strategy most would agree you need more periodization.
We are a big fan of more zone 2 work now, and later in the season adding more intensity.
But ultimately there is so many opinions on this stuff (ours seems to be more popular now and backed by more science but that does not mean it is the only solution). Partially you need to do what is fun and motivates you and if you do too much intensity for too long you will start to fall apart and the next season you might start out doing more zone 2 