This whole thing is a real shame. First, the real problem with how things have gone thus far with the DC Universe has been that it's been guided by Zack Snyder. His vision for the franchise just has not been very good. The one thing he did get right, though, was the idea of having an older Batman who has been doing the job for quite a while and is burnt out on the whole thing. Bringing in a fresh creative vision would probably solve much of what currently ails the franchise. Affleck is not the problem at all. Quite the contrary, in fact.
Second, the idea of an Affleck-directed Batman film was something that I was very much looking forward to. Now, at the same time, I can't wait to see what Reeves has in store for it, as he's a terrific filmmaker in his own rite, but Affleck is, IMO, one of our best directors working today. Him directing a Batman film could have been something truly special.
And, third, and perhaps worst of all, this means that we'll probably get some young guy stepping into the role, since the rest of the Justice League is fairly young. There are so many great stories that they could go with featuring an older Batman, but I doubt we'll get that. Even worse, possibly, we'll see Affleck's Batman handing the reigns over to a new Batman, much like in the comics where multiple people took up the mantle of Batman over the years. This is an idea that could work in the comics, and maybe on film if both Wayne and the new Batman had been built up over several films, but would be an absolute disaster if they tried it at this point in the DC Universe.
All around, this whole thing is just a disaster.