I'm a level 50bst/whm on Sylph, and i've only PT'd with this job a whopping 2 times the entire way. My experience with BST is that because you don't have to find a group, wait for groups to get going, deal with stupid pullers, wait for replacements, wait for group downtime, and hunt in overpopulated and overpopular areas you can make far more experience alone than you ever could with a group.
As of right now i'm solo'ing Cockatrice in Ozatraja, getting 200xp a kill, never stopping (I sit to heal my mana and HP after I pull another and have my pet start fighting), and getting tons of very expensive cockatrice meat and skin. If I had to group right now, i'd probably be getting less xp. Even if it was even or a little slower with BST, i'd still go solo, because this way I never have to go farm, I collect my loot while I level, the way the game (I think) was meant to be played.
The only time I ever group is during quests and with friends for the fun of it, it's just not worth it otherwise.
Just my two cents.