So is anyone casting any spells here in-between? I am guessing that the answer is no.
Lets try it this way take and generically named spells:
Player 1 - Channels 10 - Starts game with 10 mana. Casts 1 Spell Round 1 spends 5 mana to gain channeling +1 and 5 mana to gain Armor +1 (ends round with 0 mana)
Player 2 - Channels 10 - Starts game with 10 mana. Casts 1 Spell Round 1 spends 5 mana to gain armor +1 and spends 5 to gain Charge +2 and Piercing +1 (ends round with 0 mana)
Player 1 - Channels 11
Player 2 - Channels 10
At this point Player 1 has the better capability to cast larger cost spells each round, while Player 2 is ahead on offensive capabilities. After Round 6 Player 1's investment is paid back to him, also between rounds 2 and 6 he is able to get out better spells due to the increased spending capabilities provided by the increased mana generation.
That is what you have wrong. You again made player 2 cast something more that player 1 and then say player can cast more.
Both player start at 10 mana and 10 channeling.
Turn 1:
P1(20) cast mana crystal + Bridge Troll: (2)
P2(20) cast Bridge Troll(7)
Turn2:
P1(13) Cast Bridge Troll(0)
P2(17) Cast Bridge Troll(4)
Turn3:
P1(11) Bam can't cast a troll
P2(14) Cast Bridge Troll(1)
Now P2 has 1 more troll attacking your ass where is your mana benefit now?
Turn4:
P1(22) Cast Bridge Troll(9)
P2(11) can't cast
Now both player are even on amount of trolls but P5 has an extra attack over P1.
Turn5:
P1(20) Cast troll(7)
P1(21) cast troll(
+Fireball(0)
P2 has a fireball over P1 now.
Turn6:
P1(18)Fireball + Fireball (2)
P2(10)Fireball(2)
Both player are finally even
But P2 has an extra attack over P1 and an extra burn tick.
You see, until now P2 had the upper hand over P1.
Believe what you want, give bad example where player 2 spend its mana on something the other player won't, but the facta remain. A mana crystal give 0 benefits until the beginning of the 7th turn it has been cast.