Don’t get me wrong, I don’t condone or defend the use of turbo. I’m simply saying that what you described above is nowhere near the best way (you used the word “best”) to detect turbo if your basis for it mostly consists of “because he’s not mashing jabs during this time”.
The probability of it is low, yes, but the possibility is still there. To say that anyone is using turbo based on your first premise of “refrain[ing] from pressing jab or short in those instances where it makes perfect sense to do so”, and immediately confirming your suspicions because someone can lariat in succession does not mean he’s cheating. Like you said though, the probability of that is very low so you could be right in your accusation, but it’s hard to prove anything over an online game.