Roger was fine. It was never claimed that he was a good guy.
Garp didn't give a shit about things that he couldn't change and didn't participate or help the celestial dragons. He didn't go to the island to protect celestial dragons but to hunt Roger.
Oden is a wano character so automatically shit and fanfiction tier. Wano sucks, outside of Tama. The writing don't make sense and it shows.
Dragon had to suffer to make the nika retcon work. Even after that, the story still has issues and plot holes.
Whitebeard suffered from success. Not saving Oden is because wano writing sucks, as stated.
Overall, it seems that your issues are because of the writing trying to fix the hole that Wano created in the plot. Just think about it:
After the reverie people still had hopes about the plot and what would happen. But then Oda made Oden larger than life and it affected the plot more and more. First, it made whitebeard look like a asshole, then he created Yamato to steal Tama/Hyori background and fucked it more. With Nika he made the WG incompetent and to make Nika needed he made them unnecessarily evil (beyond the things we saw previously). That made characters like garp, smoker and other marines frauds. You can't even say this was planned because the holes were made later.
Like, look at this scene:
Based on what we know NOW, why Bonney running away would send shivers on Akainu spine? But, ok this can MAYBE be explained in the next chapter but one thing that he won't be able to explain is: how BB knew all this to the point of knowing that Bonney was worth 1 battleship? Everything that happened to her that could explain this scene happened in the year she left. BB would not be privy to this information and would have no way of knowing it before that since even the WG didn't knew (if she was so important she would bebetter guarded and cared of).
Anyway, everything is because the need to justify the plot holes and retcons introduced in wano.