You are right, it is NOT rock album. Linkin Park has never been a pure rock band in the first place, and they are not obliged to write a rock album for anyone. They can release a gay club dance album and it's still Linkin Park. The listeners/audience/fans CAN'T define what Linkin Park is. Only Linkin Park themselves can.
Chester is present more than 30%. Most of the time, Mike does not perform his vocals alone but they would do a duet, Chester, then Mike, or vice versa, or both of them together. Mike has some prominent rapping going on, but Chester has a huge fast singing/screaming (which people would call 'rapping') part on Blackout, and a whole song for himself that is The Messenger (that IS a Chester song, the whole 'love is my message' lyrics, the acoustic background and everything)
It's silly assuming that you know what they should do and should not do. This is THEIR band, THEIR own music. In the end, what 'artist's integrity' would be left for them if they only write lazy, easy stuff to satisfy the fans and forget to challenge themselves? You may dislike the album, it's alright, but saying that the band didn't know what they were doing is hilarious. Who are you to judge what they know?
And seriously, dear, get a life. IT'S JUST A GOD DAMN ALBUM. If you hate the album, okay, forget about it, find some other album that you love and blast it on, have a smoke, go out and take your girl to some nice dinner. Life is still good!
Oh well, they lost fans every album. And then gain tons of new fans too. Albums still sell, concert ticket sold out, videos got streamed on MTV, hits being played till death on radio. I have heard it all before. Same shit different day. Tell me something I don't know.