Great UX may make for a great tech story, but by itself it won't lead to huge traction. Great UX doesn't mean great marketing, and word of mouth. In the end, it comes down to providing something that taps into a need, and marketing. The UX part is what makes your product sticky, so people won't leave but it can't attract newcomers.
There are 2 sites that are hardly looked at in the tech space: CafeMom and SparkPeople. Take a look at them, and you can hardly say they have good UX - it's messy, and cluttered. Yet both have over 5 million uniques per month.
Great UX in and of itself doesn't mean great marketing, but it sure helps form a strong marketing message. If you can paint the picture of your product as solving a need AND being incredibly easy to use, that's powerful.
In the absence of an easy to use competitor, solving a problem is enough. But when presented with equal products, the one with a great UX will win more often than not.
I would argue that amazing UX _IS_ amazing marketing, precisely because people want to tell other people how awesome the UX is. I have a handy example: the meteoric launch of Clear.
Is this really true except for products that have a strong techie following? For me, I can't think of any product I recommended to someone mostly because of the amazing UX.
I'm not discounting the importance of UX, but it's easy to fall into the trap of focusing too much on the UX, and not on producing something people want, and finding a way to reach those people in a profitable, scalable way.
There are 2 sites that are hardly looked at in the tech space: CafeMom and SparkPeople. Take a look at them, and you can hardly say they have good UX - it's messy, and cluttered. Yet both have over 5 million uniques per month.