Mythal was betrayed by Elven fake Gods. At least that is what I thought. So her issue should be with them not us. I fell to see why she would want them to return.
According to Solas, Mythal cared for the world and it's people so even if she understood and appreciated Solas' motivation, she may still feel he is due punishment for what he directly and indirectly caused.
Solas also imprisoned the Evanuris because he thought it was the only punishment that could match the crime. Mythal may want a more final punishment for them for what they did to her if she knows how to subvert the difficulties in killing them.
You do make a good point: Flemeth seems to have no problem with the modern people or it's people so Mythal might likely share that sentiment and so not be so onboard with the consequences of tearing down the veil.