You're gonna catch a bucket edge someday" sounds like a scare tactic to me. A straight edge on a ramp tells you almost nothing about real world scraping, because what actually matters is the breakover point when you drive off a crowned lot, and that changes with how loaded you are. Guys have been eyeballing this for years and getting by fine, and if you have not scraped in 6 months of hauling, your setup is probably working better than he gave you credit for. Checking the angle once is cheap and worth doing, sure, but I would not let a total stranger at the scales talk you into thinking you have a problem you have never had.

Ha, your canvas was playing in potato mode the whole time.

Man, I feel this one in my knees. I spent years fighting tight joints thinking it was the mark of a real pro, and all it got me was lippage and a sore back from chasing lines that would not stay put. @adamr14 is dead on about the 12x24 wandering, there's just too much length on those planks to keep everything locked at 1/8 and not pay for it somewhere. Sounds like you went through some rough ones before that big plank guy set you straight and I feel for that, nothing worse than redoing work because nobody told you sooner. The grout color trick is real too, I learned that one the hard way after sweating a floor that looked fine once the grout went in.