TiZ is very useful, but not sufficient. If you watch Tim’s webinar on Fatigue Resistance, you will clearly realize that it isn’t just about spending time in the zone you are focusing on, but additionally doing the work progressively (progressive intervals: more intervals, each longer). If you do progressive intervals, then TiZ will grow.
TSS is still really important as I tried to delineate above - for overall load on the body. In addition to for individual workouts, TrainerRoad uses it by showing the progressive load differences between plans and as you go from SSB1 to SSB2, etc. The issue is that people are trying to extend its use too far.
I’ve been using WK04 for the same 3-year period that I have been using TP Premium. It is an extremely valuable and powerful tool. In the Fatigue Resistance comments above, WK04 provides Time to Exhaustion (TTE) data which tells me how much benefit I am getting from progressive intervals (i.e. pushing the PDC curve to the right). For example, when I started SSB MV1 I was at 30+mins; I pushed that to 1hr 3mins at its completion. But of course, that got hammered back down when I did my FTP test and had to raise my FTP.
The downside of WK04 is that is has a significant learning curve (i.e. you need to spend a lot of time to make good use of it). The original product is 20 years old and its not clear they have improved much in the way of the user interface. I’ve suggested to them to integrate TP Premium and WK04 into a single, user friendly product, but not clear if that is part of their product direction.
In addition to the PMC chart, I use TP Premium for its calendar and ride analysis (both much deeper than what TR provides). So it really depends on your needs and time available.