If you are on the top of your server there will not be any relegations from the level higher, because there isen't a level higher.
And the 5 Teams remaining are not tankers because only 7 can be prometed, so someone have to stay behind.
Last season i had one oponent in CL level 3, that had more 10Q that my Team, i looking for is league and he was 10th, i started to look for His opponent in league and there teams were even higher in Q, it was the league of death.
In my league he would be first without any problem but in that league he couldnt even promote, there were 12 teams full of scouts, just imagine you having a Team full of scouts and cant even reach CLs spots.
In this case those who are against tanking, would do it or not? You could get promoted and end in the same league with them, this is what happens in higher levels, even with a good Team you could be relegated because you just got unluky in the league draw.