I'd say both really.
Neither is more important than the other to me. Although footwork is the foundation and what should be conquered first, but if you don't know how to gauge distance with your hands as well, that good positioning with your feet won't mean as much because you won't get the most out of your punches. Similar to how Porter flails and smothers his work sometimes. Bradley does that to a lesser degree as well. They seem all over the place and look like they're in the perfect place to land, but they land with an inconsistent impact.
Look at Khan for example, dude been world class for a hot minute, but he's just now recently really gotten his footwork together. Dude basically got by on his handspeed and offense. Once dudes started noticing that his feet and hands didn't sync up, it was easier to take chances with countering or pressuring him.
I don't really like to look at training/rules and deciding which is more important to learn or get better at because they all play a part in making you function as a complete fighter. It's best to learn everything the right way from the jump. Perfect footwork and hand placement because they both go hand in hand. Just like you should be able to ball and drive to the basket from your left or from your right.
If you develop one aspect over the other, you'll still end up being flawed at the end of the day.