If some investor is going to ignore my traction and business just because I achieved it without signing on a token co-founder, then frankly it is their loss and I won't hesitate to politely tell them that. By definition getting to the same results without co-founders requires a much higher level of ability than if being part of a "collective". Any investor failing to recognize that is going to miss out some of the best deals and that is really their problem.
The main focus should be on pleasing customers and partners and if you do that right, eventually the right investors come along (with better terms too). Much better approach than to structure your company solely to please investors and forget what the business is all about.
You might even end up with a business making money and no investors to answer to (or at least investors not having significant control over you). What a terrible thing!
PS: Quite a few people promoted to "co-founders" should really be employees with accountability for specific tasks and projects, not an open-ended license to call the shots.