Comparing Slade to BCR is like saying that The Band sounded like Bread!!! Or that The Beatles were a bit like Dave Dee, Dozy, Beaky, Micky & Tich.
I like BCR, but they were manufactured and played other people's material, Slade were a hardworking pub band initially whose band member songwriter team of Lea and Holder elevated them to deserved fame.
They were darn good songwriters and Lea one hell of a McCartney-nesque and Jack Bruce-nesque (best of both worlds!) bass player.