I would rather vehemently disagree.
The Blood Elves have actually been quite consistently cucked by the Alliance and have held far more shaky relations with them than just about any other race. Kael openly rebelled against Garithos following his imprisonment by the Naga--add to this that the entire arc of the Blood Elves happened quite specifically because they were rejected by the Alliance and generally unable to negotiate with them. Indeed, the whole Thalassian storyline functionally happened because of a sequence of Humans deciding to be pricks, and the original High Elves themselves were also never particularly loyal to the Alliance--those that stayed loyal were the Farstriders on the frontlines, and the majority of Elves were the ones who ducked out after the Second War concluded.
Thematically, also, the Blood Elves haven't been chiefly "refined" for any of their history. They've mostly been addicts trying to recover and survive, which is a mentality which actually better meshes with the Horde, who are all in some sense survivors of odds stacked against them. The Alliance, on the other hand, are chiefly defined by the promotion of abstract moral ideals--the Blood Elves don't really have those as a central tenet of their species. Even on a religious level, their relationship with the Light is active and physical, as opposed to the abstract level on which the Humans relate with it.
Add to this that the Blood Elves have remained far closer to the Horde over their history, including that they were carried farther and through far harder times by Horde allies. Lor'Themar all but actively admits this, even considering becoming Warchief for a time. It has to be clear that the Blood Elves population as a whole are far better fit for their existing faction, and I quite frankly think that joining the Horde was a good decision from the get-go. If you've played Curse of the Blood Elves in Warcraft III, you'll notice that a lot of the Blood Elves' rhetoric lined up with Thrall's Horde, save for being considerably more amoral and pragmatic.
The only real hurdle for the Blood Elves joining the Horde would've been bad blood with one or more of the races, and the only one that ever did serious damage to Quel'Thalas would be the Trolls, and not even the Trolls that the Horde actually employs anymore. The Alliance was overall more oppressive and antagonistic to the Blood Elves--on a more macro level, it become evident why, and the Alliance are clearly not complete aggressors. However, Garithos' actions would've been enough to sour most Blood Elves, since he actively imprisoned them after giving them an unwinnable battle; when news of this reached Quel'Thalas, it is likely the Blood Elves would have blamed the Alliance more than anyone else. Younger Blood Elves would chiefly remember the Horde as the ones who bailed them out and gave them assistance in returning civilization to Quel'Thalas, whilst older Blood Elves would likely still hold a grudge against Garithos and the other members of the Alliance who made their journey to restoration so difficult. Ironically, the only strong connection the Blood Elves still have with the Alliance is with the Draenei, who were responsible for restoring the Sunwell--in this sense, it is only the new members of the Alliance who are considered particularly benign by the Blood Elves through their history.
Finally, the Blood Elves actually sticking by a faction is indicative of increasing maturity as a race. The High Elves who stuck with the Alliance were bailed out of the destruction of Quel'Thalas because they demonstrated more loyalty than the Blood Elves who simply retreated behind their shield. In this sense, it would mirror that by having the Blood Elves sticking to the Horde reward them, showing how far they've come and how they've been humbled. The Nightborne can take the role of the big, arrogant Elves now--the Blood Elves are pretty clearly at a new spot in their arc, and the days of being regal, haughty nobility behind a shield has long past.