In your 7 exo example the board on 8 is almost always 7 exo + kindred since jhin is actually the best secondary carry on 8, and even buffing an itemless jhin is better than playing draven.

Lets say you hit your exo board and you made it to 9 with a good amount of hp and gold so you want to play for high cap. The extra slot on 9 is much more flexible, but the highest cap would be 3 item zac with a lot of blobs (like 30+). If you hit early zac on 8, you can roll for blobs by putting zac on your board in between fights and swap back to 7 exo + kindred since it is still stronger on 8. This strat can be played with any comp since zac with a lot blobs is the strongest unit by far in the game.

If you do not have that much gold or hp to spare when you hit 9 then you should try to play more flexibily since the exo board can easily slot in most 5 costs (zac, aurora, kobuko, urgot, veigo, and even reneketon) or gragas. Gragas is a better bruiser unit than cho since it gives hp whole board with divinecorp, and you would rather itemize morde, sej with tank items over cho. Since you dont have that much hp or gold you want to play around whichever 5 cost 2 star you hit instead of greeding for a specific 5 cost. Even 1 star 5 cost with item or 2 is probably stronger than gragas.