I don't think giving bst native dual wield is a desirable solution.
I would rather they gave us worthwhile shields or scythes.
The problem is that there are no options which compare to dual wield for these jobs. As for Beastmaster, we have some really great Axes for pet buffs and master buffs.
I understand you want to use other support jobs. However, I don't think the solution is to just give Bst and rdm Dual Wield. It really doesn't seem to fit well. I would rather they make a fencer build for these jobs good enough to matter. And thats mostly a question of gear. I am not as knowledgeable how this works for rdm, but I am for bst.
This means there is no situation where using axe and shield is as good as using 2 axes, This is true for offensive and well as defensive play styles.
give us some shields w/ comparable pet or master buffs, and we'd be pretty golden.
Granted, Adapa Shield and Beatific Shield +1 are pretty great defensive shields. However, I can get pdt for master or pet in 2nd axe, and bst almost never tanks for lack of enmity tools. there are no shields which buff the pet.
Oh, and there's absolutely no reason beastmaster cannot dd next to pet using dual wield... it works quite well actually. Its only the flexibility of using other support jobs that has a hard time catching up.