I think this is the attitude tech accelerators are actively trying to avoid when they look for startups with more than one founder. The most important thing by far in a startup is the ability of the founders to work with other people - to be successful in an accelwrator you'll need to work with the accelerator team, other founders, investors, people you hire, and your customers. Having a co-founder or two is a strong signal that you can do that. You will have no control whatsoever over who most of those people are, or how "qualified" they might be. You have to have the ability to get on well with them and work with them no matter what.
That doesn't mean you can't be a solo founder and succeed. People do that. It just means you're much less likely to succeed in an accelerator if you can't demonstrate the ability to work well with others.
Maybe this is exclusively a networking or proximity problem but considering the tech circles I run in internationally, there just isn't an abundant amount of people I want to do business with as partners. And frankly, yes, it is because most people are woefully underqualified.
There are undoubtedly people on HN that you and I run into on a regular reading basis who have more knowledge in a random technical space than most people on the planet. There just aren't a ton of us the further you go in.
Let's not get carried away here, one person working in ANY space in the world for a short amount of time making the right decisions can very quickly become a top 1% knowledge carrier in a field with low intellectual barriers to entry. When you hear people you think are bragging about being a top person in their field, the reality is more like there are only 10,000 participants in 7 billion people on the planet, and 20% of those 10,000 are actively working on their problem.
I've considered cofounders twice, maybe three times, in my life. As far as my experience takes me, they're not frequent occurrences. You will have an expiration on how many life experiences will allow you the affordances to meet these types of people organically.
Otherwise, you need to find a cofounder through a Y Combinator-like space. And frankly, I don't see the value in that other than the immediate logarithmic fall-off of early labor split between two members with skin in the game.
So the probability space is already working against you. I'm certain there is an obvious flaw with my thinking like, having to cofounders with specialties across two spaces is undervalued, but even then you just are not going to run into enough people in your life who you're going to say, yes I want to do business with this person for 10-20+ years. Warren Buffetts and Charlie Mungers or otherwise good friends, true partners in business, are not popping up left and right. You can't pick one up at your corner store Circle K.
Edit: There are other cofounders besides technical ones, but the same truths hold across disciplines as well.