Homelander made a Maeve mistake in The Boys season 2. Despite the arrival of she-Hitler, Homelander remains the overarching villain of The Boys. Vought's top superhero killed an entire family just to silence a politician, allowed a crashing plane to fall into the ocean, and deliberately created super-terrorists to push through Vought's military agenda. Add to that the untold deaths and injuries chalked up to "collateral damage" and the rape of Becca Butcher, and Homelander is undoubtedly a horrific piece of work. But Homelander's damaged psyche presents a vulnerability, and Stormfront seized upon that weakness in The Boys season 2.
Seducing the perfect creation of her ex-husband, Stormfront conspires with Homelander to create a dominant and racially biased supe race. As his fatherly bond with Ryan deepens, even Homelander has reservations about Stormfront's views on "white genocide," but he goes along with his new girlfriend's plan regardless. Ultimately, this leads to Homelander's downfall. When the credits roll on The Boys season 2, Homelander has lost Stormfront, suffered a vast drop in public popularity, and is deprived of contact with his son. Furthermore, Homelander is forced to accept A-Train, Starlight and Queen Maeve in The Seven, ending his tyrannical control over the superhero group. Homelander bids farewell to The Boys season 2 by holding a grovelling, apologetic press conference, then playing the five-finger trumpet from the top of Vought Tower to regain some feeling of dominance.
At first glance, Homelander's big mistake in The Boys season 2 looks to be siding with Stormfront, however, Homelander's real misstep was provoking Queen Maeve. In The Boys' debut season, Maeve was disgusted by Homelander's true nature but turned a blind eye, partly out of fear and partly out of apathy. Maeve enjoys small moments of defiance, sticking up for Starlight, for example, but she remains largely powerless against Homelander's villainy. In The Boys season 2, Homelander learns about Maeve's same-sex relationship with Elena, and begins torturing the couple at every opportunity. Protecting Elena from Vought was partly why Maeve refused to rock the boat previously, but now Homelander is effectively holding Elena hostage, all bets are off. To make matters worse, Elena breaks up with Maeve after she finds out about the Homelander plane incident. Now not only is Elena in danger, but she isn't even part of Maeve's life - and Homelander is to blame on both accounts.
By involving Elena, Homelander spurs Queen Maeve to side with The Boys, and this entirely changes the course of events in season 2's final stretch. Firstly, Maeve is responsible for putting Black Noir in a coma and setting Starlight free. Without this intervention, Starlight would've been recaptured by Noir, and Stormfront's Nazi connections would never have been made public. The plan to create more supes then goes off without a hitch. Maeve takes an even more direct approach when she joins Starlight and Kimiko in a fist fight against Stormfront. It's impossible to say whether Annie and The Female could've won without Maeve's help, but her strength certainly swung the fight in The Boys' favor.
Queen Maeve's most important moment comes when Homelander is threatening to forcibly take Ryan away from Butcher. Karl Urban's trusty crowbar would've been like firing a water pistol at the Hulk, and Homelander easily could've flown Ryan to parts unknown were it not for Maeve's arrival. Using phone footage from the plane crash, Maeve exploits Homelander's desperate desire to be loved, threatening to ruin his reputation unless he stands down against Ryan, Elena, Starlight and everyone else. Unable to contemplate an ordinary life, Homelander agrees and his downfall is complete. Without Maeve, Homelander could've at least walked away from the Stormfront debacle with his son in tow, but now he faces a lifetime of Maeve using her plane footage as leverage.
If Homelander hadn't involved Elena in his machinations, Queen Maeve likely would've remained a miserable, passive alcoholic. Inevitably, Homelander overreached, underestimating how far Maeve would go once Elena's life was threatened. Perhaps if Homelander had experienced genuine love himself, he could've predicted Maeve's reaction, proving once again how important the upbringing of Compound V superheroes is in The Boys.