I’m not 100% sure of that, there are a couple of things to consider...Not a chance. There are still a bunch of Gigantamax formes which haven't gotten cards, and the fact that Legends doesn't have multiplayer means that it's even less of a "mainline game" than Let's Go. Even after Legends, we're still in Gen 8/SwSh era.
1. Not every Mega Evolution released in Gen 6 got a Mega EX card; Mega Lopunny and Mega Sableye had to wait until Cosmic Eclipse to be featured in a card and Mega Abomasnow is still MIA.
2. Certain mechanics can disappear after a certain amount of sets in an era and new mechanics can be introduced just a quickly. Prism Star cards lasted for 6 sets (5 regular sets and one holiday set) before disappearing from the TCG entirely.
On the one hand VMAX Climax (and supplementary products like High-Class Decks and VMAX Starter Sets) could finish off the Gigantamaxes’ TCG run but on the other hand they have to compete with Dynamax VMAXs for space.
I believe there are five (Machamp, Kingler, Melmetal, Appletun, and Hatterene) Gigantamaxes missing from the VMAX party.There's, like, four of them left? They could totally be squished into this set.
I don't doubt GameFreak's ability to pump out a mediocre game in nine months, but unless they do, this will shake up their regular three-year cycle. Legends introduces new forms and, very likely, new Pokemon in general. Even though competitive - which like a bus-full of people care about - stays in SwSh, this isn't a simple spin-off like Lets Go. I don't see them pumping out SwSh-related cards after the release of Legends.