JD, whether it is a good idea to run ashless TC-W rated oil in outdoor power equipment has already been determined by the power equipment manufacturers, and they are pretty much unanimous in their opinion. Their concerns with TC-W oil led to development of the JASO and ISO oil specs. What recommendations Stihl made back in the Paleozoic Era are irrelevant because the TC-W rating didn't exist them. (The earlier "TC" rated oil was good for both air and water-cooled engines.)
If you google "bia tcw site:stihlusa.com", you'll get close to two hundred hits, mostly Stihl owner's manuals that include the phrase "Do not use BIA or TCW (two-stroke water cooled) mix oils!" I assume the exclamation point means they're serious about it.
The only reason to use outboard motor oil in outdoor power equipment is to save a few bucks. Given the price of new equipment, that sure sounds like false economy to me. Stihl will double the warranty period of their tools IF you purchase a six-pack of their "Ultra" oil at the same time you purchase the tool. I'd say they really want you to use the right oil.