Marketing doesn't typically have much if anything to do with license acquisition. There's often some level of departmental crossover between marketing and product development depending on the company and the sector, but in a lot of cases the marketing department is figuring out how to best sell a consumer segment on product that's already been or in the process of being developed. Especially here, where we're talking existing IP and a familiar sector that doesn't tend to change very quickly. They're clearly not planning anything super innovative with this line if it's modeled on a line they already produce.
Mattel bid for the license when it was becoming available again. Not really a lot of options there time wise, but wanting it back during a huge DC media push under a revamped DC media strategy makes a ton of sense regardless. Because of the somewhat unusual and gradual transfer from McF to Mattel, they're limited in the product they can make at this time, so they're launching with a safe strategy they've used before: budget-friendly figures of evergreen characters in identifiable designs largely aimed at kids, their largest consumer segment. It's telling to me that the first wave is comprised of the 3 best-known characters in the Batman franchise and The Flash, who's never had much of a problem selling in general DC lines regardless of media tie-ins. (Also a character with a simple costume and common character build, allowing for easy parts reuse later in the line.)
Somewhat luckily for Mattel, Warner's pacing itself and 2026 doesn't really have a lot of DC theatrical offerings; as far as I understand it, it's just Supergirl and Clayface for movies. Clayface is a horror film written and directed by horror filmmakers releasing during the Halloween season, so kid appeal and access might be limited. Supergirl will get the bigger push, but it's female-led so it's probably not the biggest loss for Mattel to not have her in that first wave. I think they should still probably lead off with a Supergirl figure as soon as possible, because boys are still going to see that movie, but I also don't know if they have maybe dolls or something else planned for her when the film releases or if the McF transfer complicates things. I assume Todd's planning some movie figures for it.
I think you're overvaluing the action figure collector base here. Their strategy isn't foolish just because we're not the focus. We're a deeply irrelevant demographic, and frankly I think the only reason we still get big-box collector lines from companies that size is from a combination of inertia and product designers advocating within companies. Even some of the supposed collectors' lines still have a primary kid & family audience; the Mattel WWE team has insisted for years that Elite line sales are still very dependent on younger wrestling fans, which I guess tracks with the ticket prices that WWE's getting away with right now despite how visibly young a lot of their crowds are.