Flow-Rider
Burner
Never had problems getting warranty here but I get what you're saying and everyone's heard that horror story of bikes being stuck in shops for months on end waiting for warranty parts.Not only that, there are those who are short of quid, but will drop serious money to buy new bike from shop. There is this thing about "shop warranty" that they like. Oh they're professional, they know what they are doing, less chances of build going wrong, and if something is to go wrong, warranty will cover it. Yeah sure..
Not hard to research builds or manuals these days or ask a question on a forum like this before you munt a build. I've only ever bought 2 complete mountain bikes in the last 20 years, all the rest have been custom builds and only needed a dropper post warranty which I had to do AGAIN myself in any case.