about 25-30ish years ago, after Dad left Manitowoc Cranes, he worked in the test lab at Tecumseh working on 2-stroke motors for both small outboards, lawn and garden and industrial applications where they were testing various gas/oil ratios. he did the pre-assembly inspection, and did the post test tear-down and inspection in their test lab for about 6 years
they tested various oils at the time and various ratios up to 300:1. there were a few synthetics, however I believe most were dino squeezings per dad
what I remember when talking over beers, fishing, cars, etc....
the motors ran really clean at the 200:1, however died relatively quickly. at 100:1, they didnt quite meet the emissions standard, were close to lasting forever at steady state load, however showed signs of wear in when they were doing over-load and load pickup tests
at 50:1, they smoked a bit, didnt pass emissions, however were well lubricated where unburned oil would drip from the exhaust
I dont recall the ratio that they concluded (between 70 and 80:1) where the motors would survive the typical abuse with most of the oils at the time
since then synthetic oil has come a long long way, where companies like Stihl require you to use their oil. My assumption is that its more to remain in compliance with emissions than a lubricity issue.
Amsoil has some really good 2-stroke OB TCW3 oil. While I would personally run a tad closer to 75:1, they advertise it at 100:1. I would have no issue running Amsoil