@OP: Actually I don't feel anything (anything negative, anyway). This is from someone who has Cas as a Divine and took Champions of the Just (by alliance and or Conscription) route. And my Lavellan is a mage.
Everyone has their own RP reasons/perspective as to why they do what they did, and if you find that Leliana slide fits your flavour and you're happy about it then more power to you. I'm happy that a certain portion of the fan base got what they wanted

I just don't feel that "my game is
more valid than yours because of [insert reasons here]" Nor do I feel that my game with Cassandra as Divine became less valid because of Divine Leliana's slide.
In the end of the day, this is just a game where you get some control on how you shape the world and have fun in doing so.
And I'd still pick Cassandra as my favourite flavour of ice cream

cheers