5 years may be a stretch but i wouldn't be surprised with 3 more years of domination and 2 years of declining performances. taking armstrong out of the equation for obvious reasons (like the fact that he was a late bloomer
all the riders you mentioned used to race heavy racing schedules with multiple GT's per years and a lot of 1 week races and classics.
bernard hinault rode 13 GT from 78 to 86 only finishing 1st or 2nd on all them cept 1 tour where he had to withdrew (jesus christ that's impressive) plus full classics campaigns
lemond was shot by a gun and by the epo era but even with all of that for example btw 84 and 86 he rode 5 GT with to giro tour back to back rides.
big mig rode 11 GT's in his 5 dominant years!!!! with worlds, olympics and 1 week races in the middle.
contador gives the idea of racing a lot because he is always there trying to win but the fact is he has been saving his body a lot even since he stepped up in 2007. in 07,09,10 and 11 he stopped racing in july in 08 he did the easier giro vuelta double but didn't ride any of the spring classics only racing a couple 1 week races not any race after the vuelta. and he spent most 2012 benched so that's another "soft" year for him. his tougher year was by far 2010 with the giro and the tour back to back and several crashes that injured him at the tour. but that's one season out of 6.