I've used VAX and IBM systems and never heard anyone call a VAX a "mainframe". Looking into it, I get similar descriptions where they definitely were mainframe-

I've used VAX and IBM systems and never heard anyone call a VAX a "mainframe". Looking into it, I get similar descriptions where they definitely were mainframe-class but refrained from calling them "mainframes" outright to distinguish them from IBMs. Other names Super VAX, VAXcluster/VMScluster etc were common. There probably were some that called their VAX computers "mainframe" but I'd never known of one--it just has the wrong connotations. The VAX systems were actually far more advanced in most ways--except for deployment scale.