I am by no means a PvP veteran but I'll share my experiences:

• Blade Master: Lots of people switched over to Fire Build thanks to quality of life changes making it becoming more usable, and does very high damage since all its damage comes from a single skill in Dragontongue, instead of being spread on multiple skills. However from what I heard they are extremely predictable because Dragontongue needs Conflagration buff from Lunar Slash and Flock of Blades + Blade Storm in order to be spammable, and their build loses a couple of CCs. Dragontongue is also not animation-cancellable, so if you Tab Escape it they are forced to eat it, and if you tech-chase properly they're pretty much done for.
• Destroyer and Blade Dancer: In addition to their non-stop spin2win, Blade Dancer's bubble, and Destroyer's unbreakable shield and their CC immune fire puddle, their grab now unlocks a restraint skill for every other class while they hold their target up; if you don't escape this grab while in 3v3/6v6 you are guaranteed to die unless the Dest/BD is stupid enough to be standing in an anti-projectile zone and their companion's restraint skills are projectiles.
• Assassin: Received some quality of life changes with one of their knockdown skills having increased range, Summoner's Enhanced Seed Shroud added into their kit, and a 2x3 range on one of their stuns. However, they lost their blind on one of their other stuns, lost poison on said 2x3 range stun, their attacking rotation doesn't give any guaranteed crits anymore, and their ice landmine is no longer easy to cheese with since every class's grab escape on their Tab Trinket spec now removes it. They're still relatively viable overall, but still require a lot of work to get around with their cat and mouse playstyle.
• Summoner: Received a big nerf in their grab having a shorter duration and a longer cooldown so it's more difficult to cheese with. However, their party healing also got a buff, so multiple Summoners can be a big nuisance in 3v3/6v6 and just heal spam forever and keep their party living. They're much more doable since the level 45 era, but are still annoying to get around in general thanks to their healing and their cat being a prick in general and super tanky in 6v6.
• Force Master: Still very annoying to get around thanks to chill stacks, Impact block spam, Fire Storm deflect, Phantom Grip ignoring blocks, has massive range, and a block disable, lots of healing and self-freezing, and two CC escapes, making them extremely difficult to approach and keep a combo. However, they are getting a noticeable nerf toward their healing, and their Phantom Grip gets a higher cooldown.
• Kung Fu Master: Now has access to Hongmoon Rising Dragon, an 8 meter defense ignoring daze pull, which alongside Tremor (which more or less does the same thing) forces people to respect with distance. They are still very tanky thanks to their Q/E long iframes that also give them evasion buffs alongside their Counter giving them more iframes, which makes them very notorious to kill in 6v6 simply because everyone just hits into them like retards. However, they still struggle thanks to their poor openers and poor self-defense mechanisms if people simply just don't hit into their Q/E/Counter.
• Warlock: Deals relatively high damage if they can get their attacks in, but are incredibly squishy once people bypass their thrall shield, their CC/target immune field, and bubble, the definition of glass cannon. Also their thrall is just stupid and hits into undesirable stuff.
• Soul Fighter: Not too familiar with how they fare against other classes, but they are quite annoying thanks to having 6 iframes (4 of which don't need a target), a iframe bubble, strong healing, a 16 meter guard breaker, and a lot of targetless CC AoEs, so it's quite difficult to find an opening. However, once their defenses are breached they only have one Tab Trinket to escape and melee knockdown options.