Ignore the fact that rockets were unguided they were aimed in exactly the same way as the on-board machine guns the problem is once fired rockets go anywhere bar were they are meant to making them very inaccurate.
In 1944 the British conducted a test using a captured Panther painted white this was placed in the middle of a field making it the perfect target with no one shooting back at the incoming plane, a Typhoon was given the relatively easy task of strafing the Panther using all 8 rockets, this event was filmed and was at one time on youtube though I haven’t been able to find it for some time, none of the rockets scored a direct hit only one rocket landed close to the Panther and it’s not clear weather this caused the fuel tanks to rupture or if they were already ruptured either way this caused the fuel to burn inevitably burning out the tank again it’s not clear if the crew could have extinguished the burning fuel.
This was done under perfect conditions with a tank that stood out under combat conditions this would be worse the tank would be camouflaged and moving possibly with flak guns firing at the plane hence why planes destroyed so few tanks.

This is a sequence of pictures from the test.
http://www.network54.com/Realm/august27/1.jpg
http://www.network54.com/Realm/august27/5.jpg
http://www.network54.com/Realm/august27/8.jpg
http://www.network54.com/Realm/august27/12.jpg
http://www.network54.com/Realm/august27/18.jpg
http://www.network54.com/Realm/august27/21.jpg
http://www.network54.com/Realm/august27/22.jpg
http://www.network54.com/Realm/august27/24.jpg
http://www.network54.com/Realm/august27/25.jpg
http://www.network54.com/Realm/august27/27.jpg
http://www.network54.com/Realm/august27/35.jpg
http://www.network54.com/Realm/august27/36.jpg
http://www.network54.com/Realm/august27/37.jpg
http://www.network54.com/Realm/august27/39.jpg