That's just it, being first to the market is sometimes more important than worrying about competitors. They killed it so hard with the ipod that even if the zune was a better device at the time people wanted the ipod.
Doing a little digging, this was the model: https://www.cnet.com/reviews/creative-nomad-jukebox-zen-xtra... 4.4 x 3 x .86" bigger than the original Sony Walkman. It had much larger capacities and was outside the Apple ecosystem, which was an absolute feature at the time. Itunes was horrid.
USB Speeds weren't that big of a factor, though YMMV depending on the user. With the larger capacities of HD based players, you loaded once, which took some time, and then topped up with new additions which was not a big deal. My particular Nomad model had USB 2.0 though
USB 1.1 was 12mbits/s -- that is 1.5MB/s. Firewire was 400mbit/s.
Accounting only for bus speed, filling up a 5GB iPod would have taken 54mins[0] for USB 1.1 vs 1.6mins[1] for Firewire 400.
[0] 1000MiB/1024MB * 5000MB = 4,883MB / 1.5MB/s = 3255s
[1] 4,883MB / (400mbit/8) = 98s
Apple even made dual Firewire/USB cables to allow the (Firewire) charging brick to be used while syncing.