Hey man! I've been a barb player on D2R since season 1 and i can say, there are some good and not-so-good changes to barb in the current state of D2R in terms of PvP.
In terms of whirlwind functionality, since patch 2.4 implemented the FHR/Stun Nerf, you cannot stunlock your opponent anymore with tight tri-whirls so that's considered not-so-good. They removed the "ww bug" that's been happening since the days of LoD, wherein you can be "locked" on an enemy if you accidentally clicked your ww skill directly on the enemy, which is a wonderful and much-appreciated change. As for the ww IAS in current D2R patch, the overall attack speed of ALL your items will now be taken into consideration, including other sources like Fanaticism Aura, as well as hostile -attack speed sources like Decrepify, Clay Golem, Holy Freeze, etc. so you do need to also be ready for any gear adjustments you'll be needing (use this WW IAS calculator to know more -
https://warren1001.github.io/IAS_Calculator/). This is also the reason why you still need Beast in your off-hand but i think dual grief is also in a better spot now. Still, you cannot underestimate the stats Beast give you.
For dual-wielding, i believe the weapons' IAS will be averaged (rounded up) and added to the overall attack speed from all your other gears and, whether it is a good thing or not is still up for debate. Short tri-whirls, however, are i think in a better spot now as the first attack of ww now makes an attack with
both of your weapons on that first hit,
DRASTICALLY increasing DPS.
As D2R PvP matchups are still not that great compared to LoD because of how necros, druids and assassins dominate the moor, barbs can still be competitive in a controlled and tournament setting. Rules for GM maxblock (around 30-50%, depends on the tour) are being implemented across various D2R PvP groups and discords to try and make barbs a playable class. In pubs, however, don't expect to win every single time because barbs are i think the most susceptible to be BMed by others (75% block + clay golem or 75% block + mass druid zoo + holy freeze, etc). I personally still use and follow DHA's 63 FCR pvp barb guide and it still works wonders for me. But if you're going for the 40 FCR breakpoint, you may have to at least have CoA, Gface, Arreats and Kiras versus specific classes. I have circlets that doesnt even have 2os in them (basic 2/20FCR with a bit resists or stats, etc) but can still dominate.