- both numbers (1-2 pts IRL and 10+ pts in BB) are made up with no data to back them up (not your fault, these data don't exist)
The real data does due to betting markets. I'd have to double check but I believe an elite player tends to move the betting line about 6pts, an all-star about 3pts, so an average starter is probably 1pt (this is all pre-game injury).
The BB data is just a guess, but from experience it's almost certainly a much larger impact than those numbers.
I think on/off numbers would be quite accurate. For Nikola Jokić those would be 20 in 23/24 and 21.9 in 22/23. You could run several pickup games to get on/off for BB players but I doubt they're anywhere near those!