I feel like once bands have been around for a while, there can be a change in perspective. Just as you can have a favorite album, despite it having some great songs and some admittedly weaker ones, and those weaker ones don't spoil the whole album, you can have a favorite band and that band still has a few albums you feel are weaker. Or at least less enjoyable for you. But that doesn't ruin the whole band for you or anything; you just avoid those albums just as you might sometimes skip those tracks you don't really like.
I wouldn't want an entire album of songs that all sound the same. Even if it's a really killer song, once that I always crank up, I don't want an entire album of songs just like it. Similarly, I don't want all the albums by a band to be the same. I like the changes, the highs and lows, the differences in style from one album to the next.
Also, scientifically speaking, evolution occurs because of mutation. Even on my less-favorite Rush albums, there are songs I really like. And even though there are songs I really don't like, I can appreciate that the band tried something different.