I like it, but 2/4 turning to 4/6 with upgrade? That's a bit high, maybe 3/5?
time dragon (i forget name) turns into 13/4 upgraded, Ruby dragon turns into 15/2 upgraded. Air dragon turns into 13/7 upgraded and ice dragon turns into 13/6 upgraded, it fine like it is.
Dragons are made for the sole purpouse of attack, so If they had a low attack they would be useless.
(Comparing to another common summon creature, FFQ again)
Elite FFQ is in no way better than regular FFQ in terms of attack or defense. The only thing that changes is the summoning of Elite Fireflies instead of regular Fireflies (which have 1 more attack each). These have 1 more attack and defense, and the attack and defence of the elite ghoul has gone up as well.
(I am comparing everything to FFQ because It is a card implemented into the game already, and I want to see this card in as well)
Since the upgrade for necromancer (IMHO) is better than the upgrade for FFQ, I think that the upgrade should be 3/5 (a slight boost for playing one more quanta than the unupgraded)
Of course, I have no qualifications, respect or karma of any kind so this opinion is only my opionion