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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Its balanced for a few reasons mate... Inside has a hard time sniping out due to the sun, but those outside sun dwellers need to go in for the flag. Its an even trade. Outside can push in from three areas that have rotating cover if they want. They just need to do so smartly. Its a laned map. Those lanes are fairly even (one side has height advantage, the other has sun. And the sun advantage can be minimalised by lowering your brightness settings).