All the horses we've had have been started at 2. It's the common age around her to start them.
Jasper, started at 2, now 15 years old and NEVER taken a lame step.
Nutmeg, started at 2, now 14 years old and NEVER taken a lame step.
Chilly, started at 2, now 13 years old and NEVER taken a lame step.
We've had 5 other horses that were started at 2, and never had an issue with them.
Rumor, was started at 3. Put in a pasture until 5 when I purchased her. And 3 weeks into owning her, she suffered a life threatening injury that cost me thousands of dollars. ($4500+) to treat her in the past 1 year. She now is sound, but has arthritis in her hock and her future is questionable for how many years I'll get out of her.
My 15 month old will be sent to the trainer at 3 years. I'm waiting an extra year for her, but you can bet your booty I'll have already sat on her and worked her to where she will have 90% of the stepping blocks for her training already completed. I might even send her at 2-1/2, it all depends on how she is physically and mentally.
My vets have no issues with starting a 2 year old.
And my freshly started 2 years old don't canter. We do walk/trot/whoa/back for months before adding a canter in. One horse we waited until he was 3 before we added canter work.
I agree that if a horse is going to start sound, it's going to stay sound. If he's not, he's not. Horses are a gamble. Fate always wins in the end.