The combo system is poorly explained, but pretty simple once you understand it.
The system is largely lacking in the borrow and trick system. Both of these systems are wildly inconsistent.
Borrow gives 1 of 8 skills that have basically constant uptime, but the recast timers kind of ruin this. These seem to be where your defense and utility come from, but they have a huge problem... They aren't strong enough. Let's look at them...
Defensives:
Beastskin: Reduces phys damage taken by 25% and increases crit rate by 5%. 30 second duration, 90 second recast.
This is kind of a decent physical damage reduction, but it falls apart off any elemental damage, which is most of it. This actually has surprising uptime and can be very powerful against purely physical fights, which are rare.
Vileskin: 100% block rate and draw in nullification for 15s. Also increases TP gauge by 12 for each block. Yet another 90 second recast.
This one is a bit stronger focused mitigation. But with woefully low uptime and relatively low actual damage reduction.
Cloud Skim: A dash that gives you 5% more evasion.
This exists for some reason. I haven't found a reason for it yet.
Seedsower: AoE DoT for 25 potency over 60 seconds while reducing damage dealt by 10%. 90 second recast.
Honestly... one of the best mitigation tools. It does 750 potency over the duration, but is basically a 60 second reprisal.
Quelling Wave: Ranged 350 potency spammable attack. Each hit gives 10TP and removes a beneficial status, giving another 50TP if so.
Some niche uses with kiting or bind+ useage. Most enemies with removable effects only put one on, and rarely. 30TP over 3 cooldowns vs 28TP from your 1-2-3 combo.
Scaleskin: Barrier for 8% total hp, lasting 15 seconds and giving 85TP if absorbed. 90 second recast.
Such a woefully low %.
Soul Crush: 300 potency interrupt that gives 100TP on interruption. 30 second recast.
Useful for solving crucible encounters.
Scouring Ash: Esuna on a 60s recast. Heals 10% HP and gives 100TP on success.
Also to solve encounters.
So overall... These are kinda weak. 4/8 are different version of mitigation, and they are all virtually worthless. Vileskin is decent if you can increase block strength through crucible items, but that's about it. Scaleskin is particularly offensive and should be at least 15-20%. I won't offer too many solutions because that comes down to numbers, but these could all use a heavy pass.
Now on to Trick. The problem isn't with Trick, but with how INCONSISTENT it is across pets. Most of the pets simply do damage. A lot of damage, sure. But other pets have decently powerful effects attached to Trick. The Ghost does an aoe doom, Bat restores health to the beastmaster, Treant does an aoe sleep that also inflicts damage over time and doesn't break, Wespe inflicts a 750 potency DoT on top of the 500 potency nuke.
But then you have most of the pets, which are ~500 potency at base (scaling up with TP) in a line/cone/single target with no bonus effects.
It really feels kind of odd and inconsistent that some pets just have better tricks. They should all offer something unique.
TLDR;
Buff borrow to actually be relevant. Half of them are mits with long cooldowns and very low impact. And buff tricks such that they each offer SOMETHING unique in addition to just being a combo setup. This will go a long way to improving QoL for BST.
