Your subscription pays for access, there is no implied obligation to keep making it faster or more powerful. Antitrust law is intended to prevent companies from colluding or having to much market power so as to keep prices high and prevent new companies form competing in the market. This is more like a standards committee, if anything these companies limiting their LLM's power means a new company could decide to build a more powerful one and there decision does not prevent other companies, such as Chinese ones, from continuing to push the boundaries. I hope a judge tosses this case out and lets the lawyers eat the costs they have incurred so far.