Umm...unless EJ is wrong, you're wrong. You just spam AB until you run out of evocates and gems. If you have the mana (which most T10 mages should) you should never cast anything else.
I find it hard to believe that 85 will fix such heinously broken gameplay.
What you say is true if, and only if, it takes two minutes to deplete your mana pool using AB spam. That's what changes.
What changes at level 85 is very simple. Base mana will be 5X what it is now. Your mana pool will be 2X what it is now. That means that, effectively, every spell you cast costs you 2.5x as much as it does now. That makes the over-long burndown time for Arcane right now to be a LOT shorter. You simply just can't sustain AB-spam for as long. So, if you're (as an example) taking a minute to burn through your AB spam before you evocate, then at 85, you'll be taking 24 seconds. Then you evocate, and now what? Burn through your mana again? Without DPS cooldowns? Then wait 96 seconds while you do... what exactly?
Even if you're able to have a full two minutes of AB spam now, that means that you're spending, under your thesis, 3/5ths of every long fight OOM. Good luck with that.
The truth is, at level 85, you have to understand that ABspam is non-sustainable. Let's say AB spam lasts x seconds. You must then spend 120-x of those seconds not AB-spamming, and keeping a sustainable rotation going.
First, you must keep x as long as possible, in order to maximise the DPS you get from it. That means that you must start AB spam at full mana. Anything else is a DPS-loss.
Secondly, you want to maximize the damage you do during the 120-x period. So you must make a choice: Do you have that period at low mana, or at high mana? At low mana, you have a floor to your mana, so your rotation must keep it as null-mana as possible. At high mana, you have to keep your mana pool high, so your rotation must keep it as null-mana as possible.
Thusly the ONLY choice here is when you order this. Do you go x, Evocate, 120-x, or do you go x, 120-x, Evocate? The first gives you your mana adept bonus, the second does not.
Therefore, your ONLY choice for maximum DPS is AB spam, followed by Evocate, followed by maintaining a full mana pool by burning stacks. The only situation where AB-spam followed by Evocate followed by AB-spam is optimal is when X>120 seconds.