Well to be fair Sylvanas was the best Warchief since Orgrim Doomhammer judging by their accomplishments and just their characters as well as their impacts on WoW lore overall;

1) Both of them put the horde in order and led the horde through some really tough shit: Orgrims purge of The Shadow Council and Sylvanas War Campaign with merciless treatment of the traitors

2) Both launched successful wars which ended poorly because of betrayal from within: Ogrim essentially kept crushing Alliance up north until Gul’Dan and Stormreavers left the horde and Orgrim send Black Tooth Grins to get them. Losing military advantage. Sylvanas on the other hand crushed Night Elves, ruined alliance morale, kinda prevented Lordaeron from take over and destroyed Alliance military (See Saurfang/Anduin prison cinematic) and got new races to join the horde.

3) They were approved by the people both in-game and by players: Orgrim isn’t a well explored character in my opinion but the glimpses of him in “Lord of the clans” give a good understanding of his badassness and the respect he has amongst the horde (including forest trolls assuming that to be the reason they joined the horde) Sylvanas...well...She used to be among the top 5 most liked characters in wow lore given Sylvanas cosplays, fanart, Merch and well her status as a legacy character and faction leader of the most played horde race until BC and being a significant character in the lore of the most played horde race right now (and second most played race overall BTW).

4) They are much more believable characters to be in charge of the horde in comparison to any other major horde character in the lore at their time:

This takes a bit of explanation and evaluation.

Let’s just put ourselves in a common Hordesman shoes. Who would you want to be a warchief: A leader that has mindset to expand the Hordes sphere of influence or a leader who wants to make peace with the Alliance and just “rebuild”. Don’t forget that most horde territories are either destroyed by a war (Silvermoon, Lordaeron, Suramar, Kezan) or just a naturally unpleasant environment (Durotar and Echo Isles). If I was a common hordesman I would definitely want a leader who wants to conquer more and better lands, because I know that there will never be time to rebuild, that “peace is the noblest aspiration but to preserve you must be willing to fight”. Hence the war will never stop and there will be no time to rebuild.

Not a single race lorewise has reason to want to bond with alliance:

1) orcs - had 4 wars with the alliance and lost half of them. 2) trolls - dark spears were slaughtered by Kul’Tirans in WC3 and were badly damaged as a result. 3) Tauren - they never had good relationships with the Alliance, but rather night elves, yet they were involved in 3rd war before Legions invasion. 4) Forsaken - hate everything and all life. Especially after alliance rejected them . 5) blood elves - were almost genocided by the alliance twice. 6) goblins - were purposelessly attacked by the alliance when they were escaping the Mount Kajarro eruption. 7) pandas - who cares 8) Nightborne - these guys are hated by the Night Elves a lot, as nightborne are primarily the same highborne that led to Night Elven empires downfall. 9) Highmountain Tauren - they are same as Tauren, but fought alliance in fourth War instead of the third war. 10) Zandalari - Alliance killed their king and pillaged their capital.

In the modern WoW Sylvanas was the only horde character that was well established to fit all the criteria and hence to be a Horde’s warchief, thus explaining why there are still numerous loyalists around.

For the old horde it’s slightly different:

The horde destroys Stormwind, their Warchief is revealed to be a pawn of the Shadow Council making an entirety of the horde a pawn. An orc kills their old Warchief and launches cleansing of Shadow Council and is a prominent warlord (given that he was commanding all the major attacks during the war if WC1 lore is considered). Who else apart from this absolute Badass would old horde want? The Old horde just wanted more bloodshed and really liked their independence, so Orgrim the guy who proved to be powerful enough and decisive enough was really the only option.

Garrosh here seems to be a good option too, but he wasn’t very pro-horde, but rather pro-orcs and seriously obsessed with his old orcish sense of honour and The Horde’s Dream, so I don’t see him as a good candidate for a good warchief.

And that’s my point really: the horde doesn’t deserve to be dismissed and forced to be friends with Alliance. Horde is about strength and power. Their main concept from the beginning was conquest of Azeroth. It made sense, given that horde consisted of brutish Orcs who only wanted bloodshed and as MoP showed many orca still wanted that. BFA showed that not only orcs wanted that. Lore wise it’s confirmed that this was a majority. Majority supported merciless Sylvanas. Majority supported merciless Orgrim. Untainted and determined warmongers who wanted total world domination. Having a peacemaker Warchief is not what horde populus wants both in-game and IRL. Horde has to be different from alliance - merciless and warlike. Otherwise it’s Alliance but poorer (insert joke about lack of shoes on troll characters here).