Regarding the Horde identity, I can understand why the Monster Horde would evolve into the War Machine Horde.
The “hordes” of Warcraft 1 are held together by the machinations of a mysterious Shadow Council that pulls the string from behind the scenes and seems to content to just use the orcs as weapons that it can point at its enemies, backed up with dark magic and demonic allies.
Warcraft 2 goes on to reveal that the Shadow Council is comprised of these warlocks and necromancers responsible for the dark magic aspect of the Horde, so when Orgrim decides to execute them all, that leaves the Horde unable and maybe a little unwilling to rely on dark magic, though Orgrim still compels Gul’dan to provide some magical support in the form of death knights.
So, to me, it makes sense that the Horde would turn to industry and other races as a way of remaining strong after gutting its magic potential with the execution of the Shadow Council.
But the rest of the story is awful, that much is true. I see this expansion as emblematic of Blizzard’s teething pains as it struggled to transition from just making games with a little story as a backdrop to creating character-centric stories that are just as important as the gameplay, since it’s apparent that Beyond the Dark Portal wanted to be a story about a roster of heroes/villains for the Alliance and Horde, but the RTS gameplay about building bases and armies held it back and they hadn’t figured a way around it yet.
It might be worth thinking of Starcraft as a Warcraft 2.5 in this regard, where they managed to blend RTS gameplay and a character-focused story without stumbling into the same problems, before Warcraft 3 came out and they managed to make an RTS that revolved around a cast of main characters in terms of story and gameplay alike.
At the same time however, I suspect Cyberlore Studios might have been a part of the problem. Maybe they just decided to throw together some basic RTS missions that worked for Tides of Darkness, without realising the ludonarrative dissonance that they would run into with Beyond the Dark Portal’s story.
I’m pretty convinced that most of the story comes from Blizzard though, since it does make sense as their first foray into character-focused stories, which they develop further and further with their next couple of games.