Mario Kart Wii is memorable for being endlessly fun to play and replay even with groups of players that vary widely in skill and experience (ie. at family gatherings where young kids, teenage gaming fanatics, and grandparents might all be playing against each other). As a game which pits players against both each other and CPU, and which involves both randomized setup conditions/item drops and deliberate build customizations, almost every category of balance consideration comes into play in Mario Kart Wii.
Asymmetric balance comes into play in that each player begins each race at a different starting position, so those starting in first place have an automatic advantage over those starting in twelfth. The game mitigates this gap through powerful items such as the Blue Shell and Bullet Bill which only players in the back of the race can receive from random item boxes, as well as through Red Shells which target carts ahead of the shell-thrower by default.
Single-player balance comes into play in the CPU difficulty, which can be freely adjusted from race to race according to player preference or removed entirely in multiplayer races.
I’m not deeply familiar with the specifics of Mario Kart strategy, but I do know balance between strategies comes into play with Manual and Automatic drift mode. Players can choose between the two modes depending on their skill level with drifting, and when playing against opponents with a similar skill level it’s possible to win in either mode.
Lastly, balance between game objects comes into play with character choice, vehicle choice, and random item drops. While some items are significantly more powerful than others, item drop rates are partly distributed according to a player’s current position in the race, which contributes to spreading out the advantage amongst all players. Character and vehicle choice is probably where the game is least balanced — the body type of a character determines the set of vehicles they can choose from, and while each vehicle has a similar ratio of stat strengths to weaknesses, in my experience, certain stat distributions are reliably easier to win with than others. As evidence of this, when playing with more experienced players I often see them choosing from the same small pool of similar vehicles every game. However, I don’t see this minor balance issue as a detriment to the fun of the game, and I rarely see those with strong personal favorites let the minor disadvantage stop them from choosing their favorites in casual play.