I wouldn't dream of thinking anyone has anything "locked up". Certainly not OpenAI which increasingly seems to be on an uphill battle against competitors (including Microsoft who even though they're a partner, are also a competitor) who have other inroads.

Not sure what you mean by "full access", as none of the providers offer unrestricted usage. Pro gets you 2.5 Pro with usage limits. Ultra gets you higher limits + deep think (edit: accidentally put research when I meant think where it spends more resources on an answer) + much more Veo 3 usage. And of course you can use the API usage-billed model.