Tip-up can be a small fraction of a second faster.
If you do a little searching here on the forums, you will also find that tip-up can inflict nasty injuries on you. There have been at least a couple of cases reported where tip-up knives have sliced the palm of their owner's hand right open.
I have a friend who is a mechanical engineer. One of his basic rules is, "Don't fight gravity, you can't win." Tip-up carry fights gravity. Gravity never sleeps. It never tires. It simply pulls down gently on that blade, tugging at it tirelessly. Given any opportunity, it will pull that blade down and partially or even completely open the knife in your pocket.
Tip-down carry uses gravity to pull the knife shut as you carry it.
Tip-up relies on the knife being perfectly-designed, perfectly-adjusted, and carried exactly in the perfect position in the pocket. As a result, tip-up is intrinsically dangerous.
It's a tradeoff, a small fraction of a second in draw time vs. your own safety every minute of every day.
We've got some 18,000 members here at bf.c. In all the years, in all those members, I've yet to see one post saying, "I was in terrible danger and I had to draw my knife. Thank goodness I was carrying tip-up. That 1/64th of a second made all the difference. If I had been a 64th of a second slower, it'd have been curtains for me." But I have seen several posts from people who got stabbed or cut by their own tip-up knives.
You're paying a big price in your own safety for a tiny fraction of a second gain that, in practice, probably isn't gonna matter anyway.