There’s actually been some recent science on this.
Training stress metrics.
Short answer, they were all wrong in different ways.
The most accurate of all metrics. Session RPE. Basically, how hard it felt to you, the athlete doing it.
You the actual athlete have the best measurement device currently invented. How it felt, how you recovered from the effort over time. Let that always be your guiding light.
TSS alone can lead many astray. Many will not even admit it to themselves. They chase it. They chase CTL. They are both flawed metrics. If you are going to use a simple metric, use one. Use it with caution. Never let it override your own subjective feelings. They, more often than not, are right.
Is the TSS of a 5hr workout the same if you did it fasted, you crashed half way through it, you had no sleep, you just got divorced, it was 45 degrees Celsius, you forgot to drink…
TSS knows nothing about you, it’s an incredibly simple work vs time equation. We are not robots. We are complex emotional animals. All work we do is not equal. This is why TSS and all currently invented metrics fail. They need more data. Currently, they don’t have it.
You’re perception of fatigue is a skill you can enhance. Work on it.