This is why BST needs to be nerfed.
Seriously! what a really bad taru to speak like that.
Did you know that those Ark Angel fight are unique because those 3 high tier mission are all slashing damage type.
Not all Pet can be use to solo this fight because it's very difficult to do so even in normal mode if your not well gear and using the correct pet. The main Pet that was use in those fight is Swooping Zhivago bird that pet have -50% slashing damage. If SE feel that it's over power to have such a pet than nerf the PET not the BST. However, the downside to using those pet is the slow kill rate and probably require the use of Dawn Mulsum those item are costly.

First of all are you 100% sure it was SOLO and not use TRUST when double trust campaign is up? because that is not solo when using a trust. In fact, many people are using trust to help them beat normal high tier mission and others mini event.