Yes, the griffin should be at level 6, considering the stat increases (an increase of 6 on a level 6 unit looks too extreme).
And in general, if it were necessary to scale the troops further (e.g., not 6 knights against a dragon, but 10 or more), it would be logical to leave the griffins in their place and move the basic troops, i.e., perceptually, a knight is clearly not higher than a griffin.
Regarding the stat increases, I think the knight should have an increase of 1500-1200 in strength (he is the strongest of the cavalry!). :smile13: