@Background Pony #34B8
That’s why Flash and Somnambula should stay in the air around him and distract, and if possible Starswirl in his telekinesis. That’s also why Starswirl should taunt him, Tirek as already proven to be susceptible to it and it should keep him too “busy” to think about it. I probably forgot to write, but they should also avoid to all be on the same side of the dude or too static. The hardest would be bringing Tirek to the “ritual site” without what you are saying happening
(Except if I’m confusing the attack you are talking about and the one I think of, if the pillars are separated and all around, he shouldn’t be able to use on more than one at a time, allowing the pony to get back up (or be teleported a bit further away by Starswirl). The real risk of step 1, I think, would be for Tirek to catch the two pegasi in flight. Cause once done, the others would fall relatively quickly as Starswirl would tire out and once Starswirl out, none of them could continue to fight with a safety distance)

@Background Pony #8A8C
You know he could just use his shockwave slamming punch to knock out ALL the ponies within his vicinity before he grabs them for a tasty magical snack, right?

@Toastypk
I think I have an idea of a strategy they could have used (supposing than they knew that they were going to be attacked by Tirek) :
-first thing : Tirek cannot absorb magic from target that are two far, so distance attack are to be used in priority.
-second thing : staying in movement as much as possible to avoid capture.

Now character by character :
-Starswirl on diversion duty, he should use their past to keep most of the attention on himself and teleport everytime Tirek gets too close (using self-kinesis like Starlight can be good too). His second priority should be big hits (but be very careful to the others).
-Rockhoof should use his strength to throw obstacles and try and injure tirek. (If possible try and hit the head or the legs)
-Somnambula should go with the same tactic as with the sirens to distract Tirek. Flying around him, giving small hits, but on top of it recuperating potions from Meadowbrook for more direct application (notably on injuries). Thanks to Starswirl and Rockhoof, she should be able to avoid tries to catch her relatively easily.
-Flash will go with a relatively close strategy as Somnambula, except the potion part with is exchanged by him using a spear to make small cuts and other injuries for potions to go in.
-Meadowbrook will go full potions, choosing them to injure Tirek but also to help her friends hold on as the fight could take a while.
-Mistmane ane Stygian should be easily “missed” by Tirek with already five people attacking him. That would allow them to prepare a longer spell/ritual. From what we know, the pillars can’t do the stoning spell, but it is very probable than there exists other spells to get something frozen or sent him in a prepared place with protections (though those would probably just slow him down). They would prepare it a bit away from the fight to not be seen and, when it is ready, join back the fight, which would be the signal to bring Tirek to the ritual site. (To lower possible suspicion, they should say than they checked and Tirek is alone)

That second step would be the hardest as they would need to get Tirek in place without having their intentions guessed and without freezing themselves with him.

(I had far too much fun writing all of that xDDDD)

I always felt a teensy bit bad that Stygian never made it to this scene even though he’s basically their other half, but then I realized the dude would be pulverized.  
(And really, I wonder which strategies have worked against an unstoppable powerhouse?)

Steal their magic, Tirek.

Get outta my dam country, you big red BULLY!!!  
(AIRSIP FIRES AUTOCANNON FROM STARBOARD BOW ON TIREK’S BACK)  

“You can’t defeat the legendary heroes of Equestr-”  
(Tirek inhales)  
“Arrggh, we are a defeateds!”

@Background Pony #BE63  

 
Whoops, almost forgot about her - https://derpibooru.org/2135747

the hero show up, and can’t handle Tirek over a minute

STAY AWAY FROM SOMNAMBULA, YOU SCUM!

So the pillars took lessons from the royal guards - brave, combative, useless.

Why am I thinking of Cartman right now?
 
In any case, Tirek can go straight to hell.

Terick can die.

Nomnom

You’re trash Tirek

Why do ponies always just stand in front of the monster.
 
The guards and heroes have the tactical skill of a turkey-and not a wild turkey either.

Tirek sucks.

i dislike how weak they made these “legendary heroes” seem