NBSG military technology is like comparing a musket to shiny new M-4. Valks can and have been shown to use real world space flight manuvering but for artistic reasons they usually stick to atmospheric flight style combat in fighter mode. A VF-1A in basic combat load still holds a huge advantage over a viper. the viper is unarmored carries only a few missles and a pair of 30mm cannons. the VF-1 has armor harder then a tank, head lasers, nose lasers, the gunpod, and at least 12 long range missles. The overtechnology thermonuclear reaction engines of the valk give it almost unlimited endurance in space and atmospheric flight (the only valk we ever seen getting refuled as far as i know is a vf-0 which ran on over tuned conventional turbofan jets). valks can shoot down multipule missles that are incoming towards it. Vipers just dont' stand a chance for them to take out a valk they would have to out number it even worse then a typical engagement vs zentradi.