I suspect it may depend on what you consider to be alpha? I would have said that Teyla was alpha, and Elizabeth wasn't, regardless of the positions of their actors in the credits - and that Teyla was a much better match for John, therefore.
Sam definitely wasn't alpha during SG1, one of the biggest problems with Sam/Jack, for the fans I mixed with. Janet was, because she could interact with him as an equal, and tell him off when he was out of line.
Gwen has developed the habit of telling Arthur off, when he behaves badly. It still feels very much like Arthur humouring the pretty girl, though, rather than him actually respecting her opinion. I still wouldn't consider her to be an alpha. As much as I loved Arthur and Morgana's sibling relationship and don't actually ship them, from that point of view I think she's a much better match for him.
Re: From metafandom
Sam definitely wasn't alpha during SG1, one of the biggest problems with Sam/Jack, for the fans I mixed with. Janet was, because she could interact with him as an equal, and tell him off when he was out of line.
Gwen has developed the habit of telling Arthur off, when he behaves badly. It still feels very much like Arthur humouring the pretty girl, though, rather than him actually respecting her opinion. I still wouldn't consider her to be an alpha. As much as I loved Arthur and Morgana's sibling relationship and don't actually ship them, from that point of view I think she's a much better match for him.