I'm sure you can, but you may have to sandbag some fights that used to work with 4/40s or 5/50s. More people have 5* 5/65s now so it has changed somewhat.
Up to, and including, the match that says Streak=14 beforehand, it is very easy to sandbag (although I prefer the term “Unbalanced”) those last 6-7 matches by using the 3rd hero as a very lowest level hero (and in T4Alpha and T4Basic Arena is really easy, since it can be a 1* Hero). The greater the difference in rating between your 2 winnable heroes and the toss-away hero, the better chance that the opponents will be closer in strength for those 2 fights you’ll try to win.Once at Streak=15, (and for several matches) I’m not sure if full 4* 4/40 teams are sufficient (they will be after around Streak 20 or something). May need to include some 5/50 to meet an overall Rating requirement for some of those post-15 matches.So you can try continuing sandbagging beyond 15 for a while, but 4*s of 4/40 + 4/40 + 3/30 is not really sandbagging. Use 4* 4/40 + 4* 4/40 + 1* 1/1 (or a low 2* even). Not sure if that indeed still works post-15, since once I hit 15 I’ve got stronger heroes to start using then.
I'm sure you can, but you may have to sandbag some fights that used to work with 4/40s or 5/50s. More people have 5* 5/65s now so it has changed somewhat. Hey at what streak does it become infinite? I'm at 19 atm