Given the Canadian reality, I agree with you, which is why I'm advocating for that here. The disadvantage or otherwise of list PR, like STV, is that it is going to create more parties. It is going to lead to coalition governments. It does create stronger parties. It creates internally more cohesive, more united parties.
If they are not comfortable with that, parties can decide whether they want to internally democratize their candidate selection procedures or not. That will create greater opportunities for access. But that's really a different matter. That's a question of party, not electoral reform.