Yep, the split landing page will allow players to choose RS3 or OSRS. Much better than taking up space on RS3's homepage imo. Yes, it's for first time visitors (or those without cookies), but that's who it's for. Beyond that, it isn't really needed again!
EDIT: Coming back to this! I wouldn't be opposed to see more OSRS visibility on the RS homepage, but I don't think it's the most crucial thing. We have a pretty good idea of traffic coming in, where we think they want to go, and whether they made it. However, I'd love to see - braces for impact - changes made to the OSRS homepage to bring it a bit more in line with what you'd expect today. Keep the themeatics, they're key. Don't flood it with banners and ads and whatnot. But I'm sure there's more we can do to make it work better for us, you, and new players.