The "just a warm body, any warm body!" mentality is what's so detrimental about the co-founder craze. Both financially (~50% of equity!) and in terms of more risk. It's a bad idea unless they're at least as talented and motivated as you (preferably in an area that complements you), and even then it's dangerous because you give up a lot of control.
If it's your idea and your vision, why not build the prototype, get some traction, then bring on a talented employee for 5% equity? Much better than 50% with someone you met at a "find a tech-cofounder" event
I don't think its preferable to find a cofounder in an area that complements you. I think that this can be great, but what's most preferable is the right co-founder relationship. If the right co-founder is also an engineer, then that's fine. One of you should be CEO anyway, you can always hire business guys.
I think the classic mistake startups make is the duo where ones "business" and ones "technical" and the engineer ends up spending all this time building the product and the business while the business guy takes the CEO spot and controls something he doesn't understand. (assuming it's a technical business, if it's a non-technical business like a sport drink then a business guy for CEO makes sense, as sales are step key operational effort)
Are there perhaps political reasons for it? Do investors prefer having two or more founders they can divide if necessary? Does it increase "bus factor" or otherwise derisk the venture?
My opinion: two or more founders who are really invested and work well together > single founder > forced cofounder relationship. I say this as a single founder.
The hardest thing about being a single founder is cognitive load. I don't necessarily mean time. There are usually enough hours, but switching between at least five hats really strains the brain. It can also be hard to maintain energy. I find groups with other founders and working in a good startup oriented coworking space very helpful.
There are absolutely political reasons for it. Both the dividing founders reason you mentioned, plus the fact that single founders are more likely to be technical while when two people found one of them is likely to be a business founder. VCs feel they can control the business founder (or replace him if needed) much easier than the engineer, because VCs are not engineers. (and they are not entrepreneurs in my experience either, though they seem to think they are and are happy to trot out the "exits" they were vaguely involved in, usually via friends and family equity.)
I agree with your priority- a pair of fully dedicated good founders is ideal.
If it's your idea and your vision, why not build the prototype, get some traction, then bring on a talented employee for 5% equity? Much better than 50% with someone you met at a "find a tech-cofounder" event