I prefer ratios. 
Percentage of losses relative to weeks at #1.  
Sub 20% loss rate with 300+ weeks.
Djokovic -   70/387 =  0.180 <20%
Sampras  -  69/286 = 0.241
Federer    -   56/310 =  0.181 <20%
Lendl.      -   44/270 =   0.163
Nadal       -   44/209 =  0.210