the enterprise tax also always includes other features (often you don't care about those -- acknowledged and that's why we call it ssotax because "we" only want the sso portion), and is priced per-seat. it's particularly vile when removal of dark patterns is also gated behind the ssotax/enterprise tier. such as advertising to every user.
the vercel offering is a flat price per month and doesn't bring in other stuff you don't care about. it's very well priced and you pay for just the value you want. it's unfair to lump it into the concept of ssotax.