>>119596448For starters, their relationship is literally, canonically called True Love. That's enough for some people.
On another level, you've got all the crew interviews. They've outright said "we used all the same tropes as romantic lovers from past films, but made them sisters!" So you could say the dynamic is the same.
Add the people who just like yuri, and sidestep it by pointing out that Elsa and Anna were separated for their whole childhoods and are basically strangers, so it's not REAL incest.
There's all sorts of angles to come at it. But it remains a fact that their love is stronger than any magic.