Bro, while I agree with you that we havent seen much of Heather yet, everything that we have seen, is the exact opposite of beeing an alpha.
1) When she is in her wheelchair she is outraged at Tommy - he tells her to beat it and the quietly rolls on.
2) At the pool Quinn puts her in her place and she caves.
3) In the Prep Mansion bathtub, she says she doesnt wanna look at MC, girls tell her to do it, she does it.
4) Same place she says MC doesnt turn her on, girls tell her it should, she starts rubbing herself.
5) Movie night Quinn starts the anal/blowjob/threeway game, Heather becomes super insecure.
6) Sage route, MC catches her on the sofa, she gets bitchy, you put her in her place, she caves and appologizes.
I think the most natural successor - if its not Quinn - is Sarah, however, nobody knows what will happen to her if Sage finds out that she knew about Chad all along.