"The full pedal stroke" is essentially a myth. The way human physiology works, it's basically only possible to put meaningful power to the pedals on the downstroke. Studies of elite level athletes have demonstrated this - everyone mashes, and the best peddlers put a bit less downward force on the pedal during the upstroke. A bit less! They aren't pulling up, they're just not weighting it as much. Pedal stroke is super over-analyzed, and it has always struck me as a bit humorous given that it's an extremely prescribed motion that can't be significantly optimized beyond getting the positioning of your contact points (butt, cleats) just right. The benefit to clipless pedals is proprioceptive, maintaining your contact point on the pedal in the most optimal position, not the ability to put out more power throughout the pedal stroke.

I think there is a benefit to a smooth pedal stroke, but I suspect that it is in enabling more comfort at higher cadences. A higher cadence = putting power to the rear wheel more smoothly, which feels better and, depending on the rider, might be a better use of energy. But it's not about power.