Even though it had a Comic-Con-exclusive trailer in Summer 2013, remember that the for Gareth Edwards' Godzilla debuted that December, just five months before the movie opened. You can tell it got the hype train rolling because the in February 2014 drew even more views on YouTube.
Conversely, the Comic-Con trailer for Godzilla: King of the Monsters was that same day in July 2018, more than 10 months before the film opened. At no point in that long marketing campaign was the hype for G:KotM greater than it was in the wake of that first captivating trailer. The in December 2018 didn't draw nearly as many views. Even the in April 2019, just a month out from release and timed to play before Avengers: Endgame, still couldn't manage to draw the same number of YouTube views as that first trailer.
Imagine if, like G'14's comparatively more restrained marketing campaign, that first trailer for Godzilla: King of the Monsters hadn't been unleashed until December 2018. I'm not saying it would have given the movie any more staying power with audiences but in that scenario I think it may well have drawn a bigger opening weekend than its eventual $47m domestic debut. If the viewers who were wowed by that first trailer hadn't been given nearly a year to forget what impressed them about it, then G:KotM probably would have mustered at least a somewhat bigger opening weekend and thus a bigger domestic total, even with the same frontloaded 2.31x opening-to-final multiplier.
Even though Godzilla vs. Kong opens in March instead of May, I don't think it needs to begin its marketing campaign any sooner than December. The first long-range tracking for Star Wars: The Rise of Skywalker to open anywhere from $185m to $225m domestic. That would be the perfect time to unleash the first trailer for Godzilla vs. Kong, and then three months later they can cash in on that hype as much as possible.
This movie is already going to face a steep uphill climb to profitability. It's probably going to have a production budget upwards of $200m and it will probably need to surpass Kong: Skull Island's $566m worldwide box office just to break even. That's still the Monsterverse record, which I'm sure all parties were hoping would have already been broken by G:KotM but that certainly didn't happen. In that sense I think Kong's sequel really might be unexpectedly handicapped at the box office by Godzilla's inclusion. After G:KotM failed to catch on with general audiences, this crossover could end up having the smallest opening weekend of the Monsterverse. Considering how all three Hollywood Godzilla films to date were very frontloaded when they played in theaters, as were previous crossover clashes of iconic characters like Freddy vs. Jason, Alien vs. Predator and Batman v Superman, it's a foregone conclusion at this point that Godzilla vs. Kong's box office legs won't be any sturdier. It really is going to come down to just how big of an opening weekend it can manage to pull off. That's why WB is wise to make this marketing campaign shorter, like that of G'14.