Jack of all trades and master of none. will only leave you among the mediocre. It is easy to be good at multiple things, but as I said, almost everyone is good at a lot things. But a Few are the real class.
As a generalist I find myself in high demand, commanding strong rates and being in the position of building a web or mobile product from start to finish as I want.
By defintion, most people are going to be average in the field. A little extra enthusiasm, ambition, discipline and hard work will push you out of the average.
Show me one "real class" professional who only performed in one field.
More "functionality"? Better marketing? Better UI? Better traction? Better team?
Final point: it seems like you consider investment to be a necessity to build a company. It's not.
Were that the case then we'd only have one product in each market where, by your definition, the market would allow all but one to die out.
For what it is worth, I think you do need to make the product substantially better for people to check it out within a crowded market, but in a similar spirit to one of your other posts, there are multiple ways to distinguish your product (scaling, UI, feature set, etc.)