Bowie had long hair for Hunky/Hours eras with everything else in between. RHCP singer & guitarist John? Robert Plant had a short bob in the 80's. Angus Young has long grey hair past his shoulders between tours and does cut/dye for album promo. Lennon had short hair before Pepper and early 70's when he shaved his head. He had a full pony tail in some Sean photos.
Eddie Van Halen went from long ('70s to early '80s) to short (around '87) to long (late '80s to early '90s) to short (shaved in '94) to long (2000s) and then finally to short again.
George Harrison kept his hair fairly short during the 80es, grew it back towards 1998. Rick Wakeman as well.
Iggy Pop Longish hair from the sixties till around 1976, various short haircuts for a decade or so until Instinct in 1988 when he sported a weird shaggy orange mess. Short again for a while till after Brick By Brick then long ever since for the last nearly 30 years.
Roger Daltrey. He had his 70’s long hair cut circa 1982, grew it back in the 90’s and now has short hair again.
John Lennon went from hippy to suedehead in the early 70s then grew and unflattering midlife crisis bob.
Robert Smith as mentioned previously Elvis David Bowie is there a connection to be found with their hair length and their respective music?