The Focus Duration rating of an activity (or segment) is a combination of strain watts and their disbursement (work versus recovery interval durations).
Here’s one of my favorite indoor HIT workouts Say It Ain’t So - 60 which has an overall rating of Breakaway Specialist.
.
If I zoom in on the interval sets >TP I get this –
and this –
and this –
Coupled with Focus Duration is a Difficulty Score and Specificity rating.
Say It Ain’t So has a Moderate 2 diamond rating. I.e. highest score of 51 was reached at end of third set.
Finally add Specificity rating. I.e. where you spent the most time at intensity; how closely you matched the Focus Duration.
This workout — and most outdoor activities — are going to be rated Mixed.
Whether you care about FD or not, every ride has one. 
As @elcomp mentions building fitness is a given as long as TL progresses over time.
Someone at one star status increasing their training load to 3 stars will improve even if all their rides are below TP. Better way though would be to include some high/peak work even if limited to a periodic fitness test to verify the improvements.
At some point my guess is you’ll tire of 5x45s on HIT days and want to try something else.
Following XMB guidelines as a primary motivator is working well for others as noted here.