I feel like if they wanted to do a new timeline they should have just started at the beginning and did a reboot. Lore heads will want to kill me, but it would have been cleaner.
These games are definitely not meant to be a separate series or reboot by any means. They just add a layer to this "choose your own adventure" narrative design that the series has had since its very foundation in 1996.
The new remakes are not the first timeline of interpretations either. We were shown different distinct worlds through scenario systems, but the remake of the first game made substantial changes to the continuity and, in essence, spawned a new timeline. Among such changes, for example, is Nemesis, which was now being worked on since the 1980s, although in the original setting the name of the parasite was given with the idea of avenging the Tyrant from the mansion in mind. Or, for example, the Samurai Edge pistols were made by Kendo after the Mansion Incident, but in the remake they are the standard weapons of the characters.
As a result, Zero became a prequel of the remake. It doesn't work well with the original game because there is no such thing as the Clay Virus, the characterization of Rebecca doesn't make much sense, Edward didn't lose his arm, etc.
Of course, you also know about The Umbrella Chronicles that continued this worldview by utilizing Lisa Trevor and other elements of Zero and remake's lore, but at the same time also doing its own spin, like PS1 games did with "what if" scenarios.
Nevertheless, these games haven't replaced the classic ones, and stories like Death Island are truly the points where all the threads come together. For instance, the lore of the A1 gun that Jill uses in this movie states that she used her Samurai Edge pistol throughout the Mansion Incident and the Raccoon City Incident, after which she gave it to Quint for him to create the A1 model. The only interpretation that is compatible with this lore is a retelling from The Umbrella Chronicles, because, like I mentioned earlier, in the original game, Jill's Samurai Edge pistol was made after the Mansion Incident, and in the remake she left it in the town, so she couldn't give it to Quint. But at the same time, Jill wasn't infected in The Umbrella Chronicles' story, which is a key element of her slow aging and BIO5's plot, so this whole situation is an overlap of sources.
If the series needs a metaphor, then, in my opinion, the spiral is the perfect option. A spiral is not a loop, because it's a curved line that has a beginning and an end. Nonetheless, the spiral looks like a loop with its similar but distinct revolvings, just like the BIO series sometimes revisits and recites old stories in order to move forward.
Or we can choose a more relatable example: we sometimes recall events we have experienced, but we remember them differently, because our memories are not recorded footages, but a form of imagination. I think you've heard about the Mandela effect, for example.
I hope my explanation wasn't very confusing. The whole situation doesn't seem intuitive, but it makes sense when you dive into it. After all, different Japanese franchises have always had their own takes on the canon, unlike Western ones, which usually prefer a binary system when you include and exclude whole products. Capcom and Jun Takeuchi particularly want to keep all the games relevant and worth experiencing.