A stupid idea will always fail regardless of the technology supporting it. Designers nor developers don't really have any type of obligation to tell potential customers what they imagine will make them profits won't because it is a dumb idea. Don't blame designers or developers for taking your money to execute some stupid idea which they know is going to fail. That is all on customer not the technology provider.
There is no type of guarantee a site will be successful. Any type of guarantee like that is a shot in the dark for short term profits on behalf of the business provider. If anything a sites lack of profit generation would be the fault of the sales and marketing individuals who conceptualized the site in the first place and are responsible for marketing it. Marketing and sales are really a completely different aspect from creating software.
Designs nor software really generate bounce rates. It is the site/idea itself and whether it is useful which does. That goes back to sales and marketing. The exception being when a site is broken or not functioning as intended those technological attributes can affect bounce rate and profit. Could even throw some SEO into the mix but really a dumb idea will always fail.
Customers can't just expect to roll out a site and make profits or have people visit it. The site/concept has to be proven useful through R&D before a technology professional is even hired to build it. Otherwise, the site/app is destined to fail regardless of any SEO tricks or otherwise a service provider might have up their sleeve.
It really comes down to sales and marketing unless technical problems exist with the site. To that end the questions which are being asked are more applicable to sales and marketing than designers or software engineers.
I completely disagree. Not everyone is looking for the cheapest work they can find. Not everyone wants to be associated with a customer who just wants the job done and doesn't care about anything else. There will always be place for the traditional sense of a web designer. I mean most software engineers make terrible designers and vice versa.
btw things like google analytics or any analytics tool is really mostly a joke. A joke to give an impression that things are truely being tacked. When reality is I could create a fabric script to hit your site 1,000 times every 15 minutes and you would be none the wiser. Though those hits would be tracked like any others even though they were automated.
You could measure other things like for retails stores profits grossed on a website. However, that is more the accomplishment of marketing than it is the technology provider – designer or software engineer – people actually building a site.