@TheQuietMan
I think its more because Celestia is an avatar of the Sun, mean she has Power over the Sun.
Twilight is the Avatar of Magic and maybe the bigges Magican in Equestrias History.
Mean Twilights Spells are far more Powerfull as Celestias.
Other Option is, Celestia could Teleport, but she not do it on Screen.
Most time she comes oficial to Ponyville as Princess, so she use a Chariot, because her Role as Princess request the use of a Vehicle.
Theres one Scene, where Spike want todeliver a Letter to the Princess and Celestia personaly take it from him by landing on a Balcony next to him.
Possible, she has teleport to Ponyville offscreen to do this.

@Princess_Fluttershy
Celestia forgot she had a horn.

Giggle I not have read this before I made my Comment some Pages back but I had suggest him as Teacher too.^^
After all after Twilight has left Ponyville, Starlight made her Job in the School.
Still thinking if it was good for Twilight to leave Ponyville and leave her Friends behind, but in S9E26 The last Problem we saw that Twilight can Teleport herself and other to Ponyville, where Celestia had to fly.

Besides from the mane six having the ability to “summon” the Rainbow Power™ at any moment (regardless if they still have any of their normal “pony” magic); there are also other ways to “counter” Titan!Tirek that were not available back in Season 4:
. Grogar´s Bewitching Bell: This can reduce Tirek back to ZERO magic in an instant. Notice that even after being “defeated” in the Season 4 finale, he still had some remnants of his “own” magic to “give” to Twilight in the S8 finale, so this method may remove his ability to steal magic permanently (a serious threat for someone as old as him).
-> Both Pinkie Pie & Discord know how to “activate” the bell [Discord did it in both ways, having no magic of his own at that moment].

. Cozy Glow´s Seal: This is based on his own ability to steal magic & it can be set up remotely far away, in an underground fortress on the Crystal Empire´s tundra [even he could “sense” its location, he would had to fight through the weather and other passive “defenses”].
-> Besides Cozy herself, Starlight Glimmer spent at least 2 days floating above the seal in a transparent bubble (so she had a lot of time to check it out in every detail, plus thinking how it works while trying to find a way out); then if ANY pony/creature who was down there has photographic memory, they could replicate it (even if they do not understand it).

. Starswirl´s Portal/Rift: He could conjure up one on the ground as big as the one for the 3 sirens, enough for even Titan!Tirek to fall through (since aparently “flight” is not one of his abilities, given that he always had to JUMP to reach Twilight or the Pilars in combat).
-> If Tirek is automatically transformed into a human on the other side, no matter how powerfull he may had become by absorbing magic, he would now be unable to use ANY of his magic without the help of an “arcane focus” object [like how it happened with Princess!Twilight until she took control of the Element of Magic, or later the humane seven with the geods].

. Chrysalis´s Throne Shards (also the black shields/armor from the Storm King´s troops & Tempest´s cage): Whatever “anti-magic” material is made of, it could be reporpoused to negate both his long range laser beam attacks & “omnidirectional explosions”; allowing for more simpler “brute force” methods like bombarment to wear him out (eventually), or even more clever ways to just make him unconcious to become practical (like a strategical “caving down”, with rocks and water than falling on top to both restrict his movements and drown him at the same time).

. The (Malakite_gas_granade + Staff of Saccanas) combo: Even if the first only manages to crystalize one of his hooves (since Titan!Tirek is so big), as long as he remains in the same place just out of reach of the Staff, his magic will be completely drained out from him [since Tirek can NOT take out magic from artifacts, he probably has no “resistance” whatsoever against this effects], then whoever holds the staff can use all the magic without any risk of Tirek draining it again.

Too bad for you it wont.

@AwkwardLuna
Okay, you got a point.

@Wayneponeth
Considering Tirek’s MO always seemed pretty rapey to me I’m not sure if he’s actually any better.

@AwkwardLuna
Hey, there are teachers who are actually pedophiles. It could have been worse.

I’d love to be there on the first day of class.

Twilight: Students, here’s your new teacher, Mr. Tirek.

Pony raises hand.

Twilight: Yes? Question?

Pony Student 1: Why is our teacher the guy who collectively tramatized the entire country out of our magic a few years ago?

Pony Student 2: I still have nightmares…

Pony Student 3: I’m still in therapy.

Another Student in the back just cries.

Twilight: uh… because Friendship?

Oh, I want to see this go south so bad.

Professor Tirek

@angryprogrockbrony
Oh I don’t know, use her immense power to create 3 crystals for the 3 pony races to guard and put all the world’s magic inside them. If Tirek doesn’t comply, it’s doom for the world and him.

I’ll give this one to Cozy Glow. Learning from simple letters is very impressive.

He’d give out answer sheets for tests in exchange for some magic^^

Tirek: Maybe I should go back and get my teaching degree!

Appealing to his ego huh? Well played Twilight. Well played.

Great idea! Making use of Tirek’s knowledge like that.

I was exactly thinking just that. Twilight, your methods are very risky, but this is kind of too far.
You are literally giving him a chance to recover his strenght in one moment.

nagging chrissie XD

And what is Twilight’s plan if Tirek absorbs the magic from all his students?

Also I remember seeing a comic like this from a few years ago (>>1886434) where Discord opened up his own friendship school and wanted Tirek to be the magic teacher.

The Nicer 3 seem to be getting along a lot better.