Hi,
I agree about the benefits that tanking a season may give to the team.

Though,I passed my first 4 seasons with the same team I was given at the beginning,with constant but essential investments.

In the 5 season (league 5),some of my players became old,other get retired,and I had to change step by step
my team. So I repeated the 5 league 3 times.

Then,I started to invest,creating infrastructures,buying strong players,earning much more money from competitions.
Now,I'm at level 14,I've a 93.1 quality team,I earn 1 M just from tickets for each friendly match I organize ,I've many friends in lower and upper levels.
But, seeing my old opponents 2 levels over me is not good for me.

So, I'd never choose to tank a season,even to improve my team,tanking is equal to a failure.

However,in lower levels this choice can be very productive,but from level 8 you can meet very strong teams and to join the gap,you have to invest