Not necessarily
For single deck and double deck I think that HiLo performs a bit better.
According http://www.bjstats.com/bjre.asp here are some comparisons in SCOREs between KO Preferred and HiLo+I18.
KO HiLo
1D,H17,26 card cut(1-4) 34.98 33.07
1D,H17,21 card cut(1-4) 73.25 69.65
2D,H17,DS, 43 cut (1-8) 36.73 33.81
2D,H17,DS, 35 cut (1-8) 50.95 47.66
As you see, KO is slightly better for some very common 1D and 2D games.
I personally prefer KO over HiLo in single and double deck because with HiLo I would have to perfrom a TC conversion on almost every hand. In 6 deck, the TC changes less often and so I prefer HiLo.