It only makes sense.
Sport mode kick up the motor output power.
The less than 35mph in P-Mode is a bummer but necessary to keep the forward looking visual sensors from looking too far down to see obstacles ahead, and the processors have all this visual data to continuously analyze.
Nothing unexpected.
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Watching the the ever emerging videos on P4, it's been said several times that there is a power/speed trade off, and as well as making sense this should come as no surprise.