Spawnpoints convert mana and actions, totally diferent than a crystal, and they grant different options just on turn after are casted - i think nobody disagree on that, so i will forget about them for now.
We need to see if mana crystal gave different optiones, and when. I'll try to go step by step in my reasoning, more detailed, feel free to point out if i have an error or you disagree in a specific point so we can clear it out.
We can define action potencial at any moment as your mana and actions available. That's what you can use to impact the game. If you disagree with this, we can discuss it before going further.
A: With no crystal, no lair, that's what you acumulated
B: With (1x) Crystal
Turn 1
A: T1: 20 mana, 1 quickcast, 1 full action
B: T1: 15 mana, 0 quickcast, 1 full action + casting crystal
So if you don´t cast a mana crystall turn 1, you have 5 extra mana (and 1 extra quickcast). I think we all agree that first turn not casting a crystal gives you an advantage for this specific turn, don´t we? We will see next turns
Turn 2
A: T2: 30 mana, 2 quickcast, 2 full action
B: T2: 26 mana, 1 quickcast, 2 full action
Mana crystall effect is already fully taken into account in the increased channeling. At the cost of a quickcast and 5 mana, it provides 1 mana next turns.
We take no assumption on mana usage on either mage, just potential. Until turn 2, that are the actions and mana avaailable. Whatever mage B do with it's 1 quickcast , 2 full actions, mage A can (potentially) do the same with its more mana and extra quickcast. Also, there are things mage A can do wich mage B can´t do. If anyone can find a fail in the reasoning, point it
Turn 3, 4, 5, 6
Same as before... whatever mage B does, mage A can do (and even better)
A: T3: 40 mana, 3 quickcast, 3 full action
B: T3: 37 mana, 2 quickcast, 3 full action
A: T4: 50 mana, 4 quickcast, 4 full action
B: T4: 48 mana, 3 quickcast, 4 full action
A: T5: 60 mana, 5 quickcast, 5 full action
B: T5: 59 mana, 4 quickcast, 5 full action
Turn 6
A: T6: 70 mana, 6 quickcast, 6 full action
B: T6: 70 mana, 5 quickcast, 6 full action
Now both mages have same mana. I would not say Mana crystal have breaking even yet. Mage B had lost a (potential) quickcast, and, more important, mage A have enjoyed increased potential previous turns. I would say it's clear Mage A still have an (potential) edge because of its better tempo.
Turn 7+
A: T2: 80 mana, 7 quickcast, 7 full action
B: T2: 81 mana, 6 quickcast, 7 full action
Now Mage B had more mana available. Now, he can (potentially) have better plays than player A. At least, at this point there are some plays available to mage B which are not available to mage A - this is the point when you can consider Mana Crystal have give mage B an edge - but not before this point.
Of course, as previously stated, it depends on your playstyle if you value having 1 more extra mana turn 7, or you value having more potential turns 1-5. I personally think having more potential durinr turns 1-5 has great advantage (some of my games end before turn 7, almost all of them before turn 10)