Watching a vacuum leak on the datalogger when using propane or brake clean on a vacuum leak will show up instantly in dramatic swings in commanded timing and AFR in the EEC without ever generating even a 25rpm fluctuation.
If timing were fixed like on an old carburated car or maybe if you pulled the spout connector first, then absolutely rpm would jump around a lot with the introduction of fuel into a leak source, but on our cars you would have to generate an rpm fluctuation outside the EEC's ability to adapt in order to observe any rpm change at all.
I'm not saying that you can't find some vacuum leaks with propane or carb spray, but that is an extremely unreliable method of leak detection.