Prior to release and the revelation of plot details, people who loved 4 and hated 5 argued that 4 had more to do with the series because Krauser's line "All for Umbrella's sake" alluded to the plot of 6. Back then I said, and I continue to say, Capcom didn't even know what they were doing when they wrote that line.
With the details of 6's plot, we learned that Neo-Umbrella was merely a covert sub-operation run by Carla Radames, and was not related to the Organization. By the time of 6 the Organization fell apart, and Leon and Krauser's mention of Wesker confirmed that Ada and Krauser were employed by The Organization. I don't know how long before 6 Neo-Umbrella formed, but Ada and Krauser weren't a part of it.
Which brings the final point here, that 4 literally has nothing to do with the rest of the series. Moving on from Raccoon City, they abandoned any traces of a sensible viral infection for a plot that literally would never be acknowledged again in the series. All it had going for it was the behind-the-scenes subplot, which was crushed when nothing was never actually done with the Organization before its collapse. --- I am the cheese. I am the best character on the show. I am better than both the salami and the bologna combined.
4's only connection is that it introduced Las Plagas which was prominent in 5 which did have a strong connection to previous games.
RE6 was pretty unrelated to past games too despite having a lot of recurring characters. I see it more as a set up for 7 too.
Even then, the connection to 5 is of superficial importance. Uroboros wasn't related to the Majini/Plagas, so the absence of 4 would not have changed anything, really.
I'll agree about 6, but at least they made reference to the past more than just in the intro. And the other thing is that they went for a more traditional means of infection. I agree though. It's definitely the set-up for 7. --- I am the cheese. I am the best character on the show. I am better than both the salami and the bologna combined.
My understanding of 4's connection to 5 was that Wesker wanted to research Las Plagas, so he had Ada take the sample from Leon.
Given the Majini's new transformations in 5 as opposed to 4's enemies, it seems to me that Las Plagas was worked on, but ultimately forgotten when Wesker located the progenitor flowers and started work on Uroboros.
Las Plagas became sort of a "security measure" which Wesker tried to spread throughout that region of Africa to keep the BSAA off his back while he researched Uroboros.
That's how I see RE4 connecting to RE5's plot. More tenuous than most, I'll grant you, but I think RE4 still has at least minor relevence to RE's overall plot.
RE5 was definitely more important to the plot, but I'd have traded it all for a less ridiculous Wesker. --- Favourite things: Electro-swing and lactokinesis
I had the impression that Krauser was talking about helping Wesker (since Wesker was planning to recreate Umbrella) and there was nothing explicit saying that it would be carried through (and indeed Wesker gets destroyed in RE5 so the Umbrella plan failed)