imo the only reason people might have Watson below guys like Selwood, Pendlebury, Mitchell is because he hasn't played in a team that has had finals and Premiership success. Individually, Watson has achieved just as much (if not more) than those guys - Brownlow, multiple AAs and B&Fs, AFLPA Captain award et cetera. I firmly believe that if Watson had won 3 Premierships with Geelong, he'd be the unrivaled second best player in the comp.
Selwood, Pendlebury and Mitchell are massive contributors to their teams being in finals and having premiership success.