There's nothing particularly sacred about WC3, certainly not more than WC1 and WC2 which had a greater combined tenure, or WoW, which was both massively more successful and dunked on WC3 from release onwards in terms of the "Everyone is a friend now" position people bizzarely attribute to it now. Looking back though that reading gives WC3 a huge disservice, since in isolation and separate from having to lead into an MMO it's among the better stories in isolation. More importantly also because it was full of low-level personal conflict driven by character agendas as much as good and evil. The entirety of TFT is about character dynamics and internal conflict between playable factions. You have Illidan, Maiev and Malfurion/Tyrande as separate poles within the night elves, you have Arthas, Sylvanas and the Dreadlords in WC3 and then the clash between the two. These are comparatively low level conflicts compared to the RoC plot, but they're based on interpersonal, regional and factional struggles. It's just that those factions aren't the Horde and Alliance.
The Alliance, as it is in WC1-2 and then WoW is nonexistent in Warcraft 3. Jaina is essentially a tiny fraction of humanity's overall forces and representative of no one, with Lordaeron destroyed in the very first campaign. Their entire extended cast doesn't exist. The same is the case for the Horde. Every character in WC2 is gone, to be replaced with Thrall, and the Horde is the one faction that, in TFT, has no internal conflict, only an external one. The Alliance doesn't count because it doesn't exist, the Alliance campaign is about blood elves and Illidan. Unless we count Daelin, in which case it's the original Alliance being used a caricatures to beef up Green Jesus.
It's not that WoW betrays the themes of WC3, it's that the only element that carries over in terms of playable groups is the Horde, while the Alliance is an entirely new faction and the Horde, as already discussed, has had all its problems solved. Which is why it was immediately changed to avoid this problem, and the Alliance was an aggressive force in some respects - like dwarven imperialism, the Forsaken purging rule Stormwind had, the corrupt nobles and so on, all to enable the two to be in conflict. From the start, WoW has placed the factions in some form of opposition. By virtue of its gameplay, attempting to squeeze in the "We're teaming up and are friends now " thing from RoC is not viable. Blizzard realized it, but they also realize that a lot of their imagery stems from WC3, which is how we end up in this endless cycle where they realize that WC3 in WoW was never going to work, change it and flesh out the setting, then go "but muh honor, muh noblesavagery" and reverse track, then back again.
This is what BFA is, it's an attempt to default to a WC3 characterization that only worked within the context of that game. Taken out of an RTS context where the orcish story is just one of many, the WC3 Horde is just as much of a bore as the WC1/2 one, being completely one note and utterly homogeneous under a flawless leader. The same can be said of the WC3 Alliance, which is literally just Jaina in terms of carryover. All of the depth was in the other playable factions and elements that aren't such in WoW. Yet, because of how evocative those are, they are the benchmarks they're trying to drag their present incarnations, that are manifestly unsuitable for it, into that mold. When at the end of this they turn the Horde into some pantomime of WC3 Thrall's Horde despite the playable classes and races being manifestly unsuitable for it both in actions up to this point and theme, and the Alliance is already basically WC3 Jaina "Just kill my dad fam" Proudmoore, it'll be the result of this square peg in a round hole mentality that has fucked the story beyond repair to ape one element of one game seventeen years ago.