I'm guessing those that think the balancing is fine never played Mario Kart 7?
I have over 500 hours in MK7, the balancing in that game is a masterpiece. I have very few complaints with MK7, save bullet bill is nerfed (one of the worst items to get near the end of the pack). Some would argue that blue shells come out too frequently, but then good players know how to avoid them/use them to their advantage.
The important thing in MK7 is, no matter what place you're in, first place is always attainable... if you understand how to properly use items. In fact, 'rubber banding' is a decent strategy... intentionally dropping back a few spaces to (with a little luck) grab an item that allows you to take a shortcut and gain some ground.
In Mario Kart 8, no matter what place I'm in, it always seems like I get the item I need the least. The Super Star has also been nerfed, so it's no longer effective for gaining ground (and it was one of the best items in MK7). Nor are mushrooms, since it seems everyone around you is also getting mushrooms.
Also, the fact that you can't hold an extra item means you can't effectively lay traps anymore. At least, not without risking a loss of several positions.
In the end, I feel they've taken a lot of the strategy out of Mario Kart. MK8 is a beautiful game, and I enjoy playing local matches against family and friends, but when it comes to online matches, I'd rather play MK7.