I can only speak to content from the last ten years or so, but BST + MAG is a good combo. Both classes are independently strong, so together they form a decent combo. The mage can provide modest boost to the BST in the form of pet gear while buffing the BST's pet and swarm pet a bit, while the BST can boost the MAG's pet a bit.BST is the one class I'm not familiar with the inner workings of. What makes it+mage work so well? Does the BST play more of a tank role or more of a debuff/healer role?
Weird that I've never run BST, considering I like Monk and Shaman so much and it combines the two.
Buuut there's not much synergy beyond that. Without ADPS neither do that much damage, and they have limited options for pulling, CC, tanking, healing, etc. There are other combos that use BST or MAG out there over the last ten years that are better in some respects. Shd+mag or shd+bst is good. Brd+mag is good. Pal+bst or pal+mag is good. Bst+bst is also good.