One, its easier to count, but more than that its feel. Counting is the correct way to do it, knowing which gear to be in for every corner, but for us non-track junkies the gear number isn't as set for each corner and we don't have to try and think 'was it down two here, or three?' on the ever so critical corner entrance. This way we can ride by feel too, not just math. Sure, I've gone one more gear than I should have and ended up with a bike redlined before the corner exit and no more to give, and I've done the other way too and ended up putting out of the corner. But at least I had that feel of the bike and engine before I made that decision. I would rather have that then end up getting a great drive off the last corner and find now the next corner is a bottom of third corner and not a top of second corner like it was last time AFTER I let the clutch out in second (track noobs here remember).
Two, your still letting the engine spin down some in that last gear before you tip in. Blip it and let it spin down while your finishing your braking. You don't blip and downshift exactly to the RPM your going to run the corner with (not us noobs anyways), so get it done early and focus on the more important parts, like smooth throttle application, and entry points, don't try and smash all that in at your most critical moment.
The blip takes a while to learn, but is possible on near every bike. But, increase the displacement and lower the number of cylinders and the margin for error gets smaller. I can blip a 600 inline like nothing, my 1000 CC twin was a bit harder, and my single took a while to learn (yes, I blip an XRL). Just practice blipping it without the brakes, completely slowing down to 1st by engine alone. Once you get that down, work on adding some front brake in, a little at first and then work you way up. But, if you can't blip one gear at a time, what makes you think doing 2 or 3 will be better.
Now, the kicker. Not using the engine to brake is better, and typically faster, from what I have heard.