Beastmaster takes alot of exploring. Its normal that its difficult to choose a playstyle.
Beastmaster is just too versatile really. Its the challenge of an artist to "make something great" when you have so many options, choosing one is difficult.
It is the constraints of the environment that have always determined The beastmaster's strategy and tactics.
In the old-game, when charm was a thing and beastmasters could not get into a party if their xp depended on it, this meant that the you had to determine the level, species and placement of mobs in a zone.
However, in the current game I think a beastmaster is very well able to adapt to the needs of the party. Its hard to expect party memebers to be expert enough on beastmaster's capabilities though, so the challenge is understanding the party dynamics and choosing what is most needful, and sticking to it.
(I always have trouble sticking to it, because I like trying so many things with beastmaster).
You can make a nearly capped subtle blow and counter builds for Beastmaster, and have pets that support you in it(Vickie). Not just TP Drainkiss from FatsoFargann, but also Plague from Infected leech (left-yanded Yoko) and Pestilent Plume (fluffyBredo).
You can focus on magical damage from primal rend or cloudsplitter or many elemental ready moves: Charged Whisker, Pestilent Plume, Corrosive ooze, Fireball, Foul Waters, Doom Spray, Nepenthic Plunge, etc You can do some respectable burst damage and mdb down is NOT a commonly available debuff, but wonderful for any bursting fight.
Or physical damage with Decimation, Calamity, Mistral Axe, Sweeping Gouge, Pentapeck, Tegmina Buffet, Rhino wrecker, etc. though I think to do a full pet party for tody's mechanics you would be making the hard choice of choosing path D Nyame for maximum benefit.
the best tank pets I would list as Patrice(Slime), Edwin(crab), Vickie(Raaz), in general. Though Generous Arthur has fantastic support and magical defense and hp as well. Sometimes the blunt resistance and attack down from fargann is most important, sometimes the slashing resistance from Zhivago is most important.
I don't think there is a shortcut or short list for what bst can do.
Alot of people now know how good Generous Arthur is for support in a party. How many realize that Presto Julio (a VERY underleveled pet,) Can have a 4.5 minutes sleepga? also very long duration and potent aoe slow and paralyze as well?
These are immensely potent in dynamis and odyssey setups where you manage a large group of mobs. I don't think many know just how potent it is and time efficient.
Or how many know that Nihility song has the largest AoE radius of any move a player can perform? Its awesome for pulling a massive group or just a massive Aoe Dispel?
You can choose what role you want beastmaster to play in the party and do it... but you can only choose 1 role at a time typically.
Bst can even spam aoe curaga 3's with PonderingPeter. You have a 30s recast, but no mp cost. I should think that can be very valuable option if mp is an issue for say... Chaos or Obstatrix.
Did you know that ??? Needles has NO accuracy check and NO defense check at all? Falkirk and Beaztmaster made a wonderful Tolba duo video a few years ago showcasing how to cleverly apply this ability.
tldr: Beastmaster is so variable that choosing a role is very difficult, but you can do some really cool niche stuff.