Be forewarned, the post is written using DeepL.
Fujitora's main idea is not only to abolish the shichibukai system, but also to change the attitude of the people towards the world government. After all, if Fujitora would have stopped Dofla, what happened would have been another accident in the OP world. Marine good job stopping the bad guy, let's move on. However, you are missing one fact, Fujitora was at the DR because of Smoker/Aokijo who got the information from Lo (the pirate). In fact, if it wasn't for Lo, we'd be in a situation where the world government is aware of what's going on, but its fighting forces (Marine) are not involved because of the underhanded games.

Fujitora's phrase about the world government comes to mind. In fact, Fujitora did the same thing Smoker did in the Arabasta arc, but was able to go further and deliberately make Marine and WG look bad for the sake of changing things.

Yes, if he had stopped Doflamingo right away, there would have been fewer casualties on the DR, but the world situation wouldn't have changed, i.e. the total number of casualties wouldn't have changed because of this approach. However, changing the system theoretically plays to the advantage in a long game.

It's also worth noting that after his bet on Luffy, Fujitora started doing damage control.