Z.ai does offer access to DS AFAIK, so I guess that's what they mean? Maybe the feeling is that it provides more value that DS's own platform since you also get GLM, not sure.
I don't think it is the z.ai subscription that offers other models (at least I don't see any on mine). The Qwen token plan has a lot of chinese models including GLM and Deepseek and will probably be the one I use once my z.ai sub gets near the end.
Wait... you just spent 3 paragraphs singing the praises of DS... and then you say you're going to subscribe to the one that makes GLM. ?
(I do tend to agree with you, though I tend to favor GLM-5.3-flash over DS 4.1 flash.)