On the roleplaying community side as someone that rps on EU, alliance still has the bigger EU RP community, but frankly alot of horde RP has become toxic due to what id like to call "alliance rpers" moving to Horde.
But frankly from a lore POV, the Horde is finished, Ian Bates the red shirt guy has all but done the nerdiest thing ever of reading the mission table quest text and we learn how badly screwed the Horde is from that alone.
They're under attack from literally every angle and barely holding because they're all but destroyed, in eastern Kingdoms the only area lore wise the Horde has any presence in is Silverpine, The Ruins of Alterac, Dun Garogh in Hillsbrad, and Arathi besides Silvermoon obviously.
The Alliance has already retaken Southshore, Gilneas, Lordaeron and possibly Andorhal.
The Horde is struggling against a massive army from the Alliance at the Crossroads, and has been victim to Gurrellia warfare from the Alliance in Ashenvale, at Mulgore the gate to Southern Barrens is under threat by a dwarf army, Theramore is being scouted after by both armies.
And the Alliance Night Elf forces are building a "massive" retaliatory army to destroy Ogrimmar.
Yes, the Horde is in bad shape, lore wise, alot more than the Alliance even if gameplay wise, most servers have more Horde players.
In truth, its going to be the Alliance that wins the Battle for Azeroth war, because they are currently simply winning over all.
The Horde did bolster its numbers considerably with the Nightborne, Highmountain and Mag'har and soon to be Zandalari, but the Alliance also bolstered its own ranks with the Dark Irons and Kul'tirans and already had a bigger army to begin with.
Plus by the end of Dazar'alor, the capital of the Zandalar is in ruins, their fleet all but destroyed, and their people fractured and damaged more than ever.
While the Kul'tirans are united, and only lost a portion of their own fleet.