One year experience in going to the gym and you expect to see results of that of professional athletes? You can definitely get quicker by growing your legs. I've experienced it before.
Eh, no
After going to the gym for 6 months or so I bulked p and it effected my pace, mobility etc. I didn't intentionally bulk up nor needed to, its just that every week for example say bench press you would try and lift more and as a result you would naturally bulk up a bit. Mind I can go to the gym for say 2 months and bulk up easily for some reason.
As for legs, you're right, you can improve speed, mobility, the lot with leg work, but it is easier to develop your upper body over your legs so the legs are always gonna play catch up compared to other areas of your body.
My upper body bulked up at a rate of knots compared to the leg work for example.
Nonsense, man. If you've overdeveloped your upper body in comparison to your legs it's because you didn't concentrate enough on the lower body. Or just rubbish at training legs.