This is the pre-30 earnings chart, taken from a red post somewhere.
At every listed level, you're guaranteed drops equal to the indicated essence value. For reference, a champion shard costs 60% of its BE value to unlock, and gives 20% of its value when disenchanted.
6300 champion shards are worth 1260 essence, so as far as I can tell you can't get one until level 30 at least. Level 5 gives a shard plus enough essence to unlock said shard, so it can't give a 6300 shard since they cost 3780 essence to unlock.
The 6300 tier has the second most champions in the game, behind the massively bloated 4800 tier _(there are more 4800s than 1350s and 3150s combined)_.
I guess you could argue that newer champions are more 'complex', but our old 450 friend Ryze is probably more complex than half the 6300 champions.