Honestly, what will bring to table having more high tier magics?
Unless they completely blow in dmg, normally high tier magics are more mp expensive, have higher casting time, high recast time and generate a huge chunk of enmity. Would be better if it was like am with static enmity.
Higher magic are oh shiny! But it wont change a thing for the job, thus a waste of potential.
I'd give my nonexistant firstborn for higher tiers of magic on SCH.
It's true that the "normal" mages nowadays mostly resort to T1 spam. However higher Tiers have the bonus of "Alpha Strike". You can kill Outer Rakaz Skirmish Fodder in 1x T4 or T5 nuke without them scratching your face. You can 2 shot things like Kamihr Drifts mobs for EXP/CP/Eminence.
With a great FastCast set the casting time is not bad and you will kill things faster than with T1 spam due to the casting time locks.
Now if you go even further down my road you can make sets that don't swap your main weapon and thus make Occult Acumen an actual thing and making the T5 nukes give you huge junks of TP.
Then against mobs you can neglect some Macc and MAB, you use BLM Spaekona's coat +1 or Seidr Cotehardie to save you huge junks of MP.
...and then you make a nice Myrkr set with 2k+ max MP and maybe a TP bonus MoonShade to get back 500+MP per 1000TP spent.
Finally if you went down all this madness you will arrive at a point where you will actually gain MP from chain nuking T5 mobs while your full Sublimation and Convert sit there being bored. This works currently very well up to level 122 mobs. After that you might need additional MACC from your body and the nuke dmg gets too low to complete the circle.
...and while I talk all this stuff up I am just gonna fire up FRAPS to show you how it works out vs 121-122 mobs:
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