Take to bikes and leave them down the coast for a couple of months.Say 4 as cranks arent taken off regularly + tbf its a hell of a lot longer than that sometimes years or decades.
Bike A gets greased taper
Bike B gets no grease on the taper.
Torque both cranks the same[probably best to use the same model if possible]
Camp .Greasy taper- state the ungreased crank may seize on
Camp .Dry as a bone - state the ungreased crank will come off easily
Talk is cheap,the only real way to resolve this is to maybe try the above
The problem with this proposal is the "Torque both cranks the same[probably best to use the same model if possible]" bit. for the same torque applied to the threads, the greased taper will have moved further (the grease reduces the friction between the surfaces, requiring a lower torque on the tightening tool to move the same distance along the taper). So, if we torque the cranks up to the ideal torque for the ungreased setup, the greased setup will have moved further along the taper, causing plastic deformation to the softer part of the system (almost certainly the aluminium crank rather than the steel bottom bracket axle), thus permanently damaging the cranks.
I am on the "dry as a bone" side of this argument and have never yet had a crank arm seize onto a square taper bottom bracket, not in the 30+ years that I've been faffing about with bikes.
'92 Breezer Storm, '92 Breezer Sky, '93 Merlin Mountain, '94 Ibis Mojo, '96 Breezer Ignaz X, '97 (or is it '98?) Breezer Twister, Sunn Team Ti road bike
***Proud to be ordinary***