No, James Watt behaved like a sincere merchant, and he made a more powerful engine than he actually measured, in order to avoid making it again in case he complains that the engine is too underpowered.

Interesting, “It was found that a horse could conveniently raise a weight of 100 pounds attached to the end of the rope while walking at the rate of two and one-half miles per hour, or 220 feet per minute. This is 220 x 100— 22,000 foot-pounds. W att, however, in order to allow for friction in his engine and for good measure added 50 per cent to this amount, thus establishing 33,000 foot-pounds per minute, or 550 foot-pounds per second as the unit of power.” https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1466&...

It lists other estimates ranging up to 1.5 HP, and also has peak HP from one contest at 14.88HP though that was published in 1926.

PS: One even has Tredgold 6 hrs. 125 lbs. 3 m. p. h. = 1HP.

Yes, if Watt behaved like today's marketers, he would design his engine to have 25% less power than he measured and sell two engines rather than one. And he would make some screws loose to sell them again and again.