I agre on all your points @Alex it’s clear how Z2 training works. You train the body to be more efficient, use more fat, even at a little bit higher bpm. Basically you push up the floor (to use a comment of @MedTechCD Optimal Zone2 HR Target - #23 by MedTechCD)
But I’ve not understood one thing of your last comment:
Also right now for you at 130bpm might feel super easy but in 6 months of the right pure zone 2 focus it should be feeling hard, or slightly hard and intervals are appreciated at that level, so breadth wise it would feel easier than your current 135 but physically it would feel as demanding or more demanding.
Could you please clarify? I would have said the opposite