Your cited study concerns itself with power; your comment discusses force. The two are not the same. What your study is talking about is the equivalent of "horsepower". What we have been discussing is the equivalent of "torque".

Your maximum force power on a standard bike is the weight of your legs plus the force you are able to exert via muscle power and cadence.

FTFY. As soon as you consider a time component ("cadence", or strokes-per-minute), you aren't talking about force. You are talking about power.

A recumbent bike puts the rider in much the same position as the user of a leg press machine. An upright bike puts the rider in much the same position as the user of a scale.

You can only put force equal to your body weight on a scale. I'm betting that you can put force equal to several times your body weight on a leg press. Gravity does not assist the upright rider here: gravity limits the amount of force the upright rider can apply: any additional force doesn't go into the pedal; it goes into lifting the rider off the seat. There is no question that the rider of the recumbent bike has the advantage on "force".

one of which is that it’s possible to transfer MANY times more force power through the pedals

Again, FTFY. Recumbents allow much greater force on the pedals, so your comment was patently false. De-conflating "force" from "power", your comment starts to reflect the conclusions in your cited study. (Although the "MANY times" claim is still wildly misleading)

Upright bikes may be slightly more efficient at converting power, but the parent comment isn't discussing power. They are discussing force.