It may help you win the league easily but I guarantee that you will be thrown in a higher level cup and champions and it won't do any good. This is I guess the hidden rule to punish tankers. Tank only if you want new rivals, are out of tokens or have a bad team that needs a lot of players otherwise just level up since there is no big difference. After all this time my conclusion is you just need a 5 star team at the beginning of the season to be competitive with the help of some minor acquisitions. Having many 7 star players will do you more harm than good in the draw.