Particularly with your added “edit” section, it appears that your and my understanding are the same. And I do understand your point all too well regarding the decline in CTL when going from outdoor-based riding to indoor (e.g. pre-TR last summer my CTL was mid 90s and dropped to low-80s on TR). However, the converse is also true and this is where the real PMC (not a 6 week rolling average) has real value.
For reasons not important to explain here, I decided to go on a real fitness ramp (mentioned above - 3000+TSS/4 wks). That block was filled with huge TSS days (e.g. “race pace” 60-100mi w/6-12kft). ATL was in the 110-125, CTL was climbing from 60s to 80s. The real TSB (which I kept between -7 and -50) was extremely useful input for determining subsequent rides (e.g.how many days rest; how hard/long could I go). A 6 week TSS rolling average would not have been a useful metric. (and FWIW: Based on my age and related recovery requirements, I use the ATL constant at 14 days.