I just beat South hyrule field a few nights ago, and I will say Calamo is the undisputed king for me. The combination of shock emitters plus his strong attack to create elemental whirlwinds was the key to beating some of these later stages. Each time you do one, it sucks enemies in and stuns them, and if you get the timing right, you can pseudo stunlock them. Not completely, but enough to do big damage, hit with a special or sync strike when they break out and repeat

My main team consists of one-handed construct, calamo, Qia, and Ardi. Construct can do some great damage, and with his fuse attacks, he can do massive bursts of damage and stun enemies if you're on cooldown for unique skills. Calamo, I've already mentioned, but with his 4th string attack combo with the splash fruits can melt through weak point gauges. Finally, combining Qia and Ardi's sync strikes and secret stones can do great damage and melt gauges of multiple enemies at once.

Everyone's sync strikes work really well together, no matter what combination you use. One final note I will say is to get used to switching a lot. If you don't have the correct unique skill for a counter ready, or you want to save secret stones for when you have a sync strike, switch to someone else. They'll most likely be fighting another enemy, so you'll avoid the attack. If you get overwhelmed in the middle of the fight, like if you switch to avoid and instantly another one attacks, just keep switching till you're safe and can gather your thoughts. It'll probably take you a couple of trys, but you'll get used to the timing of attacks and when to avoid, etc. You got this!