To be honest, I think any character that is faster than pac-man can POTENTIALLY beat pac-man. Like sonic. If he takes that fruit he could run until time goes out, which I hate with a burning passion. Let's be careful of what we throw at sanic
Speed isn't that big of a deal. Little Mac and Falcon are both significantly faster than us. We beat Mac for sure, and I'm pretty close to saying we have an advantage on Falcon. Trampoline does massive work.
As for the stolen fruit, yes, we need to be smart. Don't throw the fruits that are easy to catch without applying some pressure yourself. There's also getting the fruit in your hand so they can't pick it up after it's thrown.
All isn't lost if a fast character gets your fruit though. Another thing to consider when your fruit is stolen is that phantom fruit will automatically work, meaning you have a very easy way to cancel your dash in smashes and tilts. As long as they're holding the fruit, the worst punishes you can take are them throwing it (mission accomplished) or a special, which really isn't that big of a deal unless you're against Sonic.
To answer the OP, I say the most important thing about Pac-Man is being able to adapt to the situation and knowing what strategy or strategies each MU calls for. You also need to know your fruits inside and out + how they interact with your hydrant water, and how the hydrant water interacts with them.