okay lets break this down because I think you are getting lost in the weeds in what I am saying and keep talking about different things.
First. Yes trying to make a Gamecube exclusive RE1 remake and the rest of the mainline titles was absolutely a bad decision in hindsight.
However as I said in my previous posts.
1. Shinji and Capcom did not have the resources at the time to make most of their games multiplatform.
They couldn't even get RE2 on Saturn and RE2 on N64 barely happened.
RE3 was pretty much a PS1 console exclusive for a year because they didn't have the man power to port it to anything else until the Dreamcast about a year late
2. Shinji's idea for Dreamcast and Gamecube exclusivity was not founded out of no where. In the early days of PS2 game developers had trouble programming for the system.
(Let me expand more on this point.)
In early 2001 when Shinji Mikami and a group of 3 other Game developers were remaking Resident Evil 1 they found the Gamecube to be powerful enough to help recreate the vision they originally had when making the original Resident Evil 1 on PS1
Capcom Entertainment announced today that it has shipped the GameCube remake of Resident Evil to retailers across the US. The game will be available in some parts this afternoon, and in others tomorrow or the day after.
www.ign.com
https://web.archive.org/web/20020602034729/http://www.capcom.co.jp/bio/making/vol07/index.html (This link is in Japanese but it is the history of RE1 Remakes development and how much they studies the gamecube at the very early development of the remake)
Now about your claim about Onimusha 2 using the same engine as RE1 remake. There is no proof of that. Capcom before the days of MT Engine's creation Capcom used custom engines for various games and seeing how RE1 Remake and RE0 were built with the Gamecube in mind first it is probably running on a custom engine that is quite different from Onimusha 2's. So even if lets say Onimusha 2 does in fact use the same engine as RE1 Remake but just heavily modified, that doesn't mean it can come to PS2 easily without making major setbacks like RE4 did. RE2 remake runs on the RE Engine but despite the Switch being able to run some form of the RE Engine doesn't mean RE2 remake can come to it unless they really diminish the quality. (Not saying the Switch situation is the same as the PS2 situation.)
Now that said even if that was the case of course the games could of been ported to the PS2 with downgrades but the point is Capcom didn't have those resources at the time and that is why very few of their games during this time were multiplaform at launch.
Shinji made a choice and while it was the wrong one looking back and I agree he should of focused on PS2 out of all the platforms. You could see why he would of wanted to work on a platform that was easy to work for.
He literally made the decision to go with Gamecube in September of 2001:
Earlier today Capcom Entertainment announced that its hugely popular…
www.ign.com
this deal was made 6 months after the release of Code Veronica X on PS2 in Japan which released on March 22nd, 2001 and nearly a month after the North American release on PS2 didn't exactly set the sales charts on fire.
Seeing a game like Code Veronica not sell on the PS2 mixed in the the programming difficulties the PS2 was giving him and seeing what the GameCube could do when they put it to the test is probably what drove him to Gamecube especially since at least they have some Japan presence.
Dino Crisis 1 sold 2.4 million on PS1 and practically nothing on Dreamcast and PC making it the best selling game in the series.
an Expensive dino crisis remake in the vein of RE2 remake would probably atleast need to 7 million to break even.
Despite Dino Crisis 2 selling a little over 1 million, and Dino Stalker + Dino Crisis 3 being huge flops you think the franchise could sell close to what Monster Hunter Rise Sunbreak did?
I just personally don't believe a Dino Crisis remake could do that unless it had serious discounts which would hurt it being a success.
Resident Evil 6 on 360 and PS3 did 9.2 Million in sales but that didn't stop capcom from nearly losing a lot of their money:
www.dualshockers.com