...or will single coil do just fine, considering all of the controls on the body of the Fender Jag?
Nothing is necessary on anything. I don't think the number of controls has any bearing on whether you prefer one type of pickup over the other. That's all it comes down to.
All about the sound you prefer, man.
Preference as mentioned and how you use the guitar for what sound you're going for. I like humbuckers in off-set guitars...thanks to Jim Root...personally.
Humbuckers aren't necessary if you prefer single coils. But if you want the humbucker sound, you pretty much need humbuckers. Humbuckers aren't any better than single coils. They are just different. If you like humbuckers, buy a guitar with humbuckers. If you like single coils, buy a guitar with single coils.
Are humbuckers even necessary... humbuckers are ALWAYS necessary! In all seriousness, it depends on what kind of music you're playing and ultimately what sound you prefer.
jaguars were originally made with single coils so I'm thinking fender didn't find humbuckers necessary.
But, presumably, they added them because they changed their mind.
This question cannot be answered. There is no right or wrong. If you want a Fender Jaguar guitar with humbucker tones, then yes, humbuckers are necessary on a Jaguar. If you don't know what kind of tone you want, or are happy with the single-coil tone, then no, they're not necessary.