A meteor is still slow compared to a missile that burns all/most of it’s energy right away (and then doing terminal in the case of dual pulse) so instead of transiting at Mach 4+ while at range, a meteor may only transit at Mach 2 let’s say. That’s a speed difference of half, which means it’ll take twice as long for the Meteor to get to an effective target position.
That means if the enemy it was fired at goes into an offensive crank, the missile will have to lead significantly more due to the speed difference when compared to a missile fired at the meteor carrying aircraft if they similarly went into a crank.
It isn’t that the missile is objectively slow, it’s that the missile is comparatively slow in transit speeds because of how it burns the motor to maximize PoK during Terminal. That gives it more of a tactical disadvantage when the missile cannot be guided by something other than the carrying aircraft, similar to the disparity between using an AIM-7 compared to the R-27ER. The 27ER arrives on target much sooner and leaves the AIM-7 dead in the water. In this case both missiles have their own seeker for terminal, however, it has to be guided to that intercept point first.
That also extends to other missiles like the PL-12 for example. The Meteor will take longer to get to a target simply because it transits slower than a PL-12 at range.