None of these dinos are true counters. If you were looking for true counters you just needed to look at the Gamepress page. These are dinos that can obstruct a Quetzorion and make it easier to kill, or that can take one out if it isn’t at full health.
Orion’s true counters are Carbonemys, Brontolasmus, Diplodocus, Allosinosaurus, Ankyntrosaurus, Carbotoceratops, Gemini, Thor and Tenrex.
No, if it went for LI first, then it can’t one-shot Dilorach, so Dilorach can slow it again. From there it’s mind games.
That’s the best strategy against Tarkus, but Tarkus can use SS then Rampage, leaving Orion with only around 500 health at level 26, since it can’t one-shot Tarkus.
Tarkus can also go for Rampage, then Long Protection, then Rampage again.
Whatever move order you use, Tarkus either beats Orion or leaves it within one-shot range of something like Monostego, or even a counter-attack from one of your counter dinos like Tryko.
It’s a similar story with Grypolyth.
As for Dsungaia, if it goes for LI and nulls the attack buff, it’ll be slower, and it’ll have taken a lot of damage. Then Dsungaia can one-shot it.