I think I was most fatigued recently on day 3 of 5, but in the middle of a very intense block of almost ninety hours in a three week period.
90 in 3 is a killer. 100 in 4 means it should be spread reasonably evenly. Working like a dog for 20 days, then 8 off is not an honest solution, but the mathematics are legal. The same can be said of other combinations. There have been airlines who had a curious process of zeroing hours at various times in a year. I'd always believed any limits were rolling limits, just like my body/brain combination. I couldn't zero my tiredness. That trick may not be allowed anymore, but it shows the true attitude of the puppeteers. FTL's need a sensible human touch. Many are never that lucky. FTL's are productivity driven = money. EASA administrators are heavily lobbied by the financial gnomes. The debate is not a balance of forces. It needs to be. I have friends in the many of the more traditional airlines than I worked for. Annually they are as productive as I was, less tired, better remunerated and the companies make handsome profits. Where there is a will there is a way; and it needs discussion and agreement from both sides of the workforce. They work hard and are treated well.
Sadly we are not the only victims of the last 2 decades of industrial greed, there are so many others in a variety of industries.
I'm not a aficionado of labour practices, more of human behaviour; but I wonder if the general demise of unions and the rise of fat cats and all out financial power in a variety of industries is just a coincidence.