Handling is relevant to grip. Grip is relevent to how fast you can get out of/in to the corner. Handling is relevent to how fast you can get out/ in to the corner. More grip = faster cornering speed as well. Cruising at 50mph ruins the corner speed so you can only do 50mph through the corners. Thats not a test of handling. Not completely anyway. Not accurately...
But speed is a factor which is produced by the HP, if one car can gain .1 secs on a straight away how is it possible to use lap times as an example of which one turns better