The core business for each of the 5 will not be companies like yours, but rather few hundred to few thousand companies each who exclusively use their model not for technical reasons, but because they were wined and dined or due to bundling with another service. The other hundreds of thousands of customers are all bonus. This is true for most categories of SaaS not just LLM inference.
If the vendor of a core piece of software that you are already locked into tells you they are raising prices and adding AI inference features, you are going to cancel whatever AI plan you have and use theirs. Or pay the amount anyways (which is even better business-wise for them).
Eventually, semi-random differences that arise in their distribution may end up informing model capabilities as well, and _that_ is when true model-level differentiation may happen. But this is not necessary and if it comes true would just be a bonus.