This is the most broken comp in the game, mostly due to the fact that you can hard stabilize on even Ahri 1* with 6 Sentinel and that you can go for these exact same Ahri items every single game (and you should). Once you find Ahri 2 and Blitz 2, you're insanely stable, and you can play for a high cap with 5 costs like Qiyana and Sona.
Sentinel chosens are broken since they allow you to play a very straightforward gameplan. Corki is a great item holder, but other holders include Annie, Seraphine, Kaisa, and Senna.
To get through stage 3, just add more Sentinels and then either True Damage, Big Shot, KDA, or Superfan depending on what you hit.
Stage 4 Rolldown
Very important for this comp and with this meta- GO 8 AND SEND IT AT 4-2 (if you're rich enough, you can even do 4-1).
Roll for the final comp, best case you hit Blitz Sentinel chosen, you can also settle for one of the 3 cost Sentinel chosens and then swap them out at 4-5.
If you hit Ahri, great. If not, Lulu or Seraphine can continue to item hold for Ahri into stage 5. Like I said earlier, even 1 star Ahri is stable early stage 4, but you need to have 2 star Ahri to be stable stage 5.
Positioning-wise, be sure to put your Spark in front of Ahri, the shred is very important on her. Always play Sona over Seraphine since she makes your team scale insanely well with time.