There is a lengthy thread on the adjustments made to workouts since the move to Systm.
Why have workouts been made easier in the new Systm app?
Thin Air is noted by some (including me) as potentially needing the ftp numbers bumped up by around 10 - 11% to bring it back close to the original Suf version.
@Coach.Neal.H offered a pretty comprehensive explanation on why many of the workouts had been adjusted, this included an assessment of users actually completing sessions.
I suspect that the old TA would have had a very high failure rate as sustained efforts are probably the most challenging type of workout for many.
I regard sustained efforts as being a real strength, and my best 20min effort still remains a TA session from around 10 months ago. Having said that, I recall I still had to pause a couple of times to catch my breath before continuing.
Next time I do TA I expect I will bump up my ftp numbers, but certainly not by 10% - more likely 5%