I'm not sure about your scale of punishment. There's needs to be both carrot and stick:
1) Full admission and immediate disclosure on being caught, without any recourse to stupid stories and evasive answers about beef, beer, dogs, wife's illness, being the most tested athlete, etc. - results in one year ban.
2) Denial followed by the same full disclosure as in '1', ie: what, where, how, who knew, where were they obtained, who paid for them, who was complicit, who chose to turn a blind eye, etc - would result in a 3 year ban.
3) Continual denial or reluctant admission but no full disclosure of all the facts and circumstances, - then life ban.
I can't accept that the riders act alone, but they are the one's that get clobbered. We need to weed out all their accomplices who make the doping world function.