I'll keep it short since I'm on mobile.
Don't judge story by gameplay because it's not rational; thank you plottwist.
Furthermore Trevor and 3 other people defeat Dracula in CV III. This mode of switching players is based on CV III. POR is irrelevant because it's the exact same scenario, switch between 2 characters, but canonically all the protagonists are fighting together.
C4 I'm not really fussed if you believe the non-narrative endings to be canon, but there's only one REAL ending for each game. The reason I don't consider what I believe are "non-canon" endings (the ones which don't continue the story) to be canon is that you have to then consider every non-canon ending to be canon. The only time I consider this is if a plot/ narrative/ timeline can actually continue (see my signature) OR when the plot makes sense and stops the player from doing what they shouldn't be able to do i.e.
- Sisters mode in POR is canon, they can't beat Brauner and the story doesn't allow it.
- Richter and Maria mode in POR is non-canon for obvious reasons.
- AOS' Somacula ending is non-canon because then DOS can't happen.
As for my final say on the Julius/ Dario debacle, first of all its canon, so we all need to get over it. Secondly, using a VK with little to zero power(rage) is like using the whip of alchemy. Leon wasn't weak, but he couldn't beat Walter. Death got rid of Walter in 5 seconds, and with the VK at full power, Leon was able to beat Death. The truth and the canon shows us that the VK's state makes a huge difference to the state of a Belmont's power. The VK was left in Castlevania to weaken the entire damn Castle, that's overly substantial power. Facts>emotion when it comes to rationalising narrative.
This brings me to the next point that compared to AOS, the plot in DOS well it sucks. Soma nearly becoming the Dark Lord is a fair plot point, but a lot of the story is reaching; Julius<Dario, The Castle bring a carbon copy of Castlevania (despite people pointing out it may be LOI's Castle), Dmitri and the whole Menace scenario, the narrative was not as good as AOS. They wanted to make another Sorrow title, and however the plot unfolded it would have probably been weaker than AOS imho.