Is using commercially available yeast to create a sourdough starter effective?

It is certainly possible to culture commercial yeast using the same method as a sourdough starter, but adding the yeast at the first step: see e.g. Culturing Yeast in Dough and Baking lots of bread - keeping a yeast starter. Your starter will also pick up natural bacteria, giving it some of the sourdough tang.

The commercial yeast, Saccharomyces cerevisiae, will, at least in the short-term, out-compete any wild yeasts that drift in, so your starter will not have the diverse strains of yeast in a sourdough starter. (See the section on yeasts in https://en.wikipedia.org/wiki/Sourdough and http://microbialfoods.org/yeast-profiles/.) I expect you will still make good bread, but it may not have the same depth of flavour as sourdough bread made with a mature wild yeast starter.

There are many instructions that tell you to begin sourdough starter exactly as I think you are suggesting, to add commercial yeast to the initial water and flour to give it a jump start. It gives you a jump start and you can begin using your starter much sooner. It is not a true sourdough, yet, as a sourdough is normally defined as a self sustaining living starter which is from local wild yeast balanced with the complementary bacteria which give a distinct texture and taste. You will not have that. But note, in the early stages of using a new sourdough start, you also have not achieved that balance yet either and the results are still pleasant if not as nice as they will be later.

You absolutely can do this. The results will be a little harsher and faster acting rise than the subtle, slower action of a mature sourdough. You will be more prone to early success and then a start that dies. If you use too much yeast to begin, it will quickly burn out, use too much of to feed and then starve, or your environment might not be right for it to sustain. The commercial strains tend to be very reliable for immediate use, but less tolerant of long term environmental variation, so fail more often when using them to create a sourdough starter from all reports I have seen and from my experimentation. If it works, your sourdough will change over time as your local wild strains will slowly be captured and replace the commercial strains as they are more suited for your local environment. If you keep it going long enough, you will eventually end up with exactly the same starter you would have had you only captured wild strains to begin with, it will simply take longer because it will be slowed by the wild strains needing to displace the domesticated ones. They will, it just takes time.

Some will say nonsense, you just can't do it, but I personally have and have seen others. I kept a starter begun that way for about 4 years. I would not do it again myself unless I lived in an environment that I had repeatedly failed to get one begun "correctly". From memory, I think it took almost 2 years before that starter was at the same place a wild strain started one made it in maturity in about 3 months. From that point on though, you could not tell the difference between the two. Myself, I would not want to wait 2 years for it to mature to that level, but others might. For those who say no though, I would point that common advice given to boost a slow initiated starter is to add things like rye or other whole grains. This works by adding a boost of yeasts from the whole grains. These are still outside, introduced yeasts. They may be a lot closer to your local strains, but unless that whole grain was grown in your location, they are not the same strains, so exactly the same process occurs. You artificially boosted the yeast colony from outside sources to get going, and then that outside original colony is slowly displaced by local. In this case, you are starting closer to the final colony, and the transition is much easier and quicker, but the process is the same. Starting with a fresh or dry sample of someone's start from another area, again, exactly the same process.

I like getting the the final balance sooner. But when I lived in the desert and got discouraged, I used the technique and it worked. What I could bake after a month I thought was OK, after two years was very good. When I tried again and started the more traditional way, what I had after a month was good, after 3 was very good.

There's overlap between wild yeast and the commercial kind: A recent study performed by the Wolfe lab in the Department of Biology at Tufts University, which uses fermented foods to study microbiomes, showed that the dominant yeast species in most sourdough cultures is Saccharomyces cerevisiae—the very same species used in store-bought yeast. Here is one study: https://pubmed.ncbi.nlm.nih.gov/33496265/