Problem is, you're not supposed to look at the rankings that way. A player's ranking at any particular time, gives an indication of his form over a decent period of time. So the top 20 rankings of all time don't give a measure of how good batsman X was, it shows the highest peak in form that batsman X has ever had. Since Tendulkar has been more reknowned throughout his career for his consistency, rather than his brilliance over a short period of time, its naturally going to underrate him. Lara's rating is a little harder to understan, but I think it can be attributed to the fact that his brilliant performances have been pretty spread out over a long period of time. Plus, he'll often make big scores after extended lean patches, so when he's in form he has to make up for the lower rating he had before.
If anything, Yousef's current rating just shows how excellent of touch he's in right now. It doesn't necessarily mean he's a great, after all Vaughan had a great run of form too earlier in his career, but you can't say his career has marked him out to be a great.