RE lost its forward momentum after the RE 3.5 to RE4 deal and you may notice how Capcom quickly filled the Chris gap thereafter
Sesha.
CVX is a mainline game (further written by Flagship unlike RE3), Rev 2 has him as part of the Raid mode and I overlooked Zero, he did skip that 2002 offering after all, but the
only mainline game outside of Zero between REmake in 2002 and RE5 in 2009 was RE4. It may be a masterpiece but it didn´t have to be an RE game as
everything got put on a bus there which further shows how little Mikami cares about game writing. The plot of RE1 mostly forced on him so he just said fuck it all the next time he got free reigns. I wonder if he would have even used Leon if there wasn´t so much RE 3.5 footage out there. Not that I can complain.
The only thing he wasn´t there for was the fall of RC as he was off in Europe, I think.
Chris already started to fill up his continuity gap in 2007´s UC where he gets top billing. Him and Jill lead the last Raid on Umrebella there, he witnesses the death of Spencer in RE5 (LiN) in 2006, he is a founding member of the BSAA in 2005, he is the reason the underfunded BSAA teamed up with Blue Umbrella, etc.
Why he joined Blue Umbrella, from
Crimson Head Elder´s translation of the Samurai Edge ALBERT.W.MODEL 01 pack in material:
A lot of products and experimental data left by Albert Wesker were once again inspected in-house by the rehabilitated Umbrella Co. and were extremely effective in redeeming most of the old Umbrella Corp.'s dark legacy.
The anti-B.O.W. research results in particular mesmerized the researchers. You could call the fruits of that research the ultimate handheld weapons.
The results of basic research into renouncing biodiversity are included within, but we've excluded them in this document.
Part of the research envisioned combat in an unaffected state; alongside much conceptualizing of practical use by skilled combatants not equipped with weapons of mass destruction like viruses.
In a paper among his personal effects, he argues that weapons of mass destruction don't necessarily lead to improving the situation.
Unbound to the old regime, the "Blue" researchers have summed up those research results and are conducting development based on mass-production; to be supplied for testing to anti-biohazard units such as the B.S.A.A.
A major benefactor of the BSAA was TRICELL (and thus Wesker), complete BSAA units were killed on-screen as late as in Vendetta which is set in the mid-2010s and Blue has the best weapons. What we see in RE7 (NaH) is probably just a BSAA unit under the employment of Blue Umbrella.