I think that "blunders" and "failures" seems a bit harsh for some of these
In a lot of cases, the TOC were operating a combination of routes that didn't neatly fit into one name, so sometimes you need to be a bit vague - e.g. I wasn't a huge fan of First Capital Connect but you've got to recognise that it wasn't just the old Thameslink franchise, it was the "GN" bit of "WAGN", so to call the whole thing Thameslink might have confused people who'd previously associated all Thameslink trains as running across the river, which obviously wasn't going to be the case on a 313 into Moorgate
Avanti might sound daft, but what sensible and short name is there for it? Call it London Midland & Scottish if you want, but that'll annoy the Welsh (given that the franchise runs to Holyhead, as well as upsetting a few Scots who'd contend that it's making a third of the British land mass equivalent to one English city or one English region!)
Few TOCs fitted nearly into geographic boundaries (e.g. Thames Trains running to Gatwick, East Midlands Trains running to Liverpool, Northern running to Nottingham... just as the Northern Line serves the most southern station on the London Underground, but nor the most northern station!) - what's more important is a simple brand that people can understand (e.g. not every Cross Country service goes from one coast to the other, but people get the gist)
Other than Valley Lines and Island Line - those were both pretty simple names that explained what they did pretty well!
"One" is probably the most derided brand, but it was an attempt to show that it was combining Anglia, Great Eastern and the "WA" bit of WAGN, so I can see why a unifying name got the nod - it's just a shame that they went for the one that they did, because some other things about the franchise were quite good - I liked the way that each bit of the franchise had a separate colour scheme, but with a unifying livery of lots of stripes at the ends, to show that it all belonged together, that was a worthwhile idea
Doesn't matter what you brand a franchise though, some "witty" enthusiast will manage to spell something unsavoury out of the letters - you've got to ignore that kind of nonsense when coming up with a brand