With that initial Collider report stating Reeves was in heavy talks with Jake, I'd always thought that was for an earlier iteration of the film where it covered Batman's mature years. Sort of as a smooth transition from Batfleck even though it's technically its own thing. Looking back, it doesn't sound as plausible. This Y2 angle seems so laser focused and feels like the only path Matt wanted to take.
I can absolutely buy into Matt wanting to "lock down" a major part like Joker early on. Especially with actors who have several months/years of projects already underway, making scheduling difficult. This was about a year before Rob was even in the picture, but Joker is such a special role it's not unfathomable it could have been cast first. I don't imagine it to be the type which requires the normal chemistry test anyway.