Michael is right.LOL! Just use Servo-AF or "EyeTracking / Continuous" or whatever it is called on your camera for handheld wide-open portraits. Model and/or photog can wobble around, focus will still be on cornea ... or on eyelash ... at worst ... grrr ;-)
Even a "cheap" Canon RF 85mm lens should be f/1.8, not f/2.0. Following your observations, the T-value should be even better compared to the old EF 85/1.8 with T/2.1.
I'd find a Canon RF 85/2.0 only worthwhile if it was as compact and light as the Pentax smc 77/1.8 Limited - L 48 x D 64 mm, filter 49mm (!), 270 grams - despite full metal construction and including built-in sliding metal lens shade.
FYI, at 2 m to subject, 85/2.0 vs 85/1.8 DOF:
85/2 lens could be made small and light.... there is an obvious advantage for studio / controlled light. what the heck would you need a huge 85mm lens for when you shoot stopped down to at least F8 anyway?