I don't mean to negate whatever negative experiences you've had, but I'm running a campaign now that started at level 1 and is now at level 16, and I've never seen the system "flop hard" or not work.
It's not perfect, I admit. The issue of the party having too little to do with their gold has been a problem. If there's a truly serious flaw in 5e, IMHO it's that. I've had to do too much as a DM to fill in that gap that the rules as written left. But even there the game never "flopped", or "didn't work", or anything close to the wording you used. If that's been your experience, I'm so sorry! But that sounds more like a bad DM or bad table than the fault of 5e as a ruleset.