I suppose it depends a lot on what you mean by 'indie'. Morrissey's mainstrem success has been pretty limited. With the exception of Quarry hardly any of his albums have sold over 100,000 copies and some less than 50,000 which is tiny in terms of mainstream success. There are lots of 'artists' who've been going for years who easily sell a million records like U2, Oasis, Red Hot Pepper, etc. I guess other more indie types of his generation might be considered to be bands like New Order who used to sell tons but now sell about as many as Moz.
Moz has been fantastically successful as a cultural phenomenon but pretty feeble as a mainstream musical force...
Morrissey maybe hasn't achieved so-called mainstream success in terms of CD sales, but no one can deny the longevity of his music.
Morrissey is continuously attracting new younger audience which is amazing.
Razorlight got 60,000 audidence last year's V Festival, but in next five years I doubt they'll still have those audience.
20 odd years later Morrissey still has 20,000 audience which proves he's very successful.