Batman is not reduced. If anything the character is made more complex because different aspects are brought to the fore by different actors.
The fact is that it is almost impossible for any one actor to capture the full complexity of a real human. The nearest film has ever gotten is Orson Welles playing Charles Foster Kane and even that was a thin shadow of the real William Randulf Hearst.
The best you can get is if a character is played by more then one actor if you look at all portrayals you get the full complexity of the character. When you are dealing with a written character who has existed for almost one hundred years this can be even more the case. Taking batman as an example Keaton captured the dangerous obssesed side of Batman that was always brooding, for all of the problems with the script Kilmer captured the Batman who was worried about Robin becoming like him and wanted to see him avoid the path he took, Clooney again despite problems with the script captured the father and son like bond Bruce Wayne has with Alfred, Bale captured Batman as the crusader who is working out larger plans and doesn't want to just scare people and doesn't want to do this for the rest of his life, he capture the Batman who wants to inspire people to stand up on their own.
None of these actors on their own capture the full Batman character but when taken together they come close and each one focuses on what that actor was good at showing us, the same with the Bonds.
I really don't think we need a timeline that links them all and I still enjoy the Bond and Batman films as stand alone films with only a few links between them. The Indy films so far have very few links between them as well and the only reason Temple was a prequel was because Marian wasn't in it, there was no real character or plot reason it had to be a prequel and a lot of people still don't know that it was because they missed the one little caption in the film informing them of this fact. Also there is the fact that if you make a film with all the Indiana Jones qualities everyone is just going to call it a knock off so if it is produced by the rights holders why not just call it Indiana Jones? I would prefer that instead of being asked to pretend it is not an Indy film. I am not saying you are wrong to feel the way you do but what happened with Star Trek was the result of bad writing, it didn't mean that the idea can't work and as long as they don't remake the old films or say they never happened then all they are really doing is giving us more adventures with the same character. So I don't have a problem with that.
I understand how you feel and I am not saying you are wrong but for me I think I would find it distracting if I was asked to pretend that a movie that is in every way an Indiana Jones movies is not an Indiana Jones movie just because the actor was recast. It would be as if Henry the forth part one and two were made into the films and then when it came time to make a Henry the fifth film there was flashback scene with Fullstaff but because the producers could not get the actor who played the character to come back they changed the character's name.
Also for me in the films Indy has already been played by another actor in The Last Crusade, and it was for the exact same reason we are talking about recasting here. Ford was too old to play the character taking part in an adventure taking place in the year it was set in. Ford is clearly too old to play Indy in any movie that would be set during or just after world war two so I have no problem with them recasting again.