Richard, might I inquire how long you've been playing TF2? It doesn't sound like you fully grasp how the game flows and what players enjoy.
Now that we fully understand what it is you want, let me provide some points as to why I believe it's an unwise idea.
Having CPs before the final one provides "checkpoints" of sorts that gives the attacking team some sense of accomplishment. Without them, if they lose they will feel as though the entire round was fruitless and they accomplished nothing. This will result in an un-fun map that people won't wish to play.
To look back into history, in Team Fortress Classic most maps of this type only had the final CP (dustbowl only had 3 CPs, one for each stage). After ten years of development and testing on TF2 Valve obviously determined it's better to have checkpoints along the way to let the attackers feel they have made progress.
By extension, when we received payload these checkpoints provide a limit to how far back the cart can reverse. Again this helps with the psychological aspect of playing because the attackers know they cannot lose that ground once gained.
If you remove these checkpoints and allow the battle line to flow across the map from one end to the other you might as well be playing a map like Granary designed for both teams to push forward.
The stages are far too small to separate into their own map. Servers usually have maps change every 30-45 minutes, and nobody would want to play a single stage of a map over and over for that long. This is exactly why server admins usually set arena maps to have a smaller timelimit. This leads to my next point...
Switching teams is good. It gives people a chance to play a little different and see the other side of the action and experience the map in a different way. Keeping teams the same will only make playing the same stage over and over again much much worse. In their current multi-stage style, moving from stage to stage keeps things interesting and enjoyable even though you are still on the same side of the fight.
Lastly, why would anyone want to play these? What is the convincing argument to play much smaller, more repetitive, less attacker-accomplishment versions of these maps when they could instead play the full map as it was intended and is accepted by thousands of other players?
Although this point wouldn't matter if these were completely custom maps and not edits of existing maps, they would still suffer from all the previous points.
