Why would you compare PS+ with Game Pass? You should compare PS+ to Gold members.
GP should be compared to PS Now, which was 3.2M last year. (Cant find a more up to date number than that)
But there's tremendous room for growth
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PS Now is, admittedly, a footnote on the list of PlayStation services these days – but its number of subscribers has been gradually growing. As of the end of March this year, the service had 3.2 million members, which is dwarfed by
PS Plus' ginormous 47.6 million – but is almost double where it was at the same time in 2020.