To make it short:
The burning shrine is not balanced at all.
It is a thousand times harder to snipe someone from inside, while they're outside.
This actually applies for all sorts off combat.
In addition it is quite hard hitting someone with things like lightnimg grenades from inside, while it is incredibly easy to land one on people who are approaching from the inside.
Some might say that you can just rush outside from the inside soawn, but the team on the outside can get there faster.
TL;DR
The burning shrine is unbalanced
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You can wait in the back heavy area to pull the outsiders in and then beat em that way