If the Nara's group of probably four to six ready fighters manages to fight off an entire squadron or more of Tev strikecraft, there's a serious breakdown on at least one level. The entire complement of a Nara WILL NOT be ready for an incursion. Keeping the entire complement of pilots ready round the clock is, in a word, dangerous. Sure, you'd have ready-five wings, but they still won't be ready to intercept. All it takes it knocking off the cannons or doing some other significant damage to make them rotate off the line. There aren't near enough Naras in Sol to absorb even light casualties and keep a blockade up.
If the Tevs follow up with any capital or corvette presence at all, the blockade falls apart, and the balance resumes with the UEF in a worse position following the necessary repair and refit of perhaps as much as half of the remaining Nara presence in Sol, without even mentioning Karuna casualties.
Tevs can afford attrition. The UEF can't, not by any stretch of the imagination.
EDIT: And also what Hades said.