I get your point (and Lol's). Yes, I'm aware of the complicated history of 10cc, and for a myriad of reasons too numerous and confusing to get into here, we will never get a concert 10cc reunion of Kevin, Graham, Lol and Eric. The closest thing to that is when Kevin makes a guest appearance with Graham and the band, which happens every once and a while in England (and is great to see). There actually was an attempt at a reunion for Glastonbury within the past decade, though it ultimately didn't go through.
Personally, I feel that Graham, being a founding member, songwriter and one-half of the continuing duo that kept 10cc going through the latter seventies and eighties, has the right to use the name (and unlike other bands, it's not like they've fought over the use of the name, as none of the other members have any inclination or desire to tour.) And better yet, they are fantastic live, doing those songs justice and properly crediting Kevin, Lol and Eric for their wonderful songs and music throughout the set.
I saw no one at the show complaining that they'd felt duped it being Graham's band (and no Kevin, Lol and Eric present). If anything, the fans know enough of the band's history to understand exactly what they are getting - Graham, Rick Fenn and Paul Burgess (both of whom have been in 10cc since the seventies) and several other longtime talented musicians.