The 'from scratch' part was mainly to distinguish the difference between creating a new engine for a home console game, over something like some of their lower budget 3DS sequels they were working on at the same time, like Phoenix Wright 6. Which I left out of the equation for that reason. They don't even make changes to the UI there. So as much as they had re-used animations in Marvel Infinite, it's still in a different league compared to games like that. Especially considering the licensing they had to do with Marvel.

That's still not true, because Marvel Vs. Capcom wasn't from scratch, it was made with Unreal 4.  Marvel Vs. Capcom 3 was made with MT Framework, which had been in use since 2006?  So that's not a new, from scratch engine, either.  I really don't understand what you mean, to be honest.

Assets can be reussed even in different engines I believe.

Still I think he is just pointing that this game had a lot more game put into it than a sequel in the same gen.

Resident Evil 3 used pre-rendered backgrounds, so to get those different angles still took days to process. 

Sure, but probably they were worked together for a good bunch of time.

If memory serves, Resident Evil: Code Veronica was renamed (It was supposed to be resident evil 3) Because Sony had a deal with Capcom to have a resident evil trilogy released on the PS1.  Resident Evil 3 was developed probably by an outsourced studio.  Of course they had access to everything used in RE2's development, but rendering the same scenes at different angles no doubt took a while.

Remake 3 isn't going to have pre-rendered backgrounds, and will take place in much of the same areas as resident evil 2.  Items like handguns, cranks, etc don't need to be redone either.  same area, same time period.  Some things will be marginally different as the setting collapses to the zombie outbreak, but these are minor things that aren't the same as creating entirely new areas and scenes.

So RE3's development time really shouldn't be a surprise to anyone.

Yep not surprised by the time it took, but agree with Hiku that Capcom moved from tight budget to taking their bets and collecting the prize.

Had no idea RE3 was outsourced, I did love it.

Not that it's important, but it says here that RE3 was developed internally by Capcom. It was just a different team than before.
https://en.wikipedia.org/wiki/Resident_Evil_3:_Nemesis#Development

Though about REmake 3, I haven't played the original in a long time, but I feel like it mainly takes place in different environments. I skimmed through a speedrun on the original RE2 and RE3 to refresh my memory, and that seems to be the case. I'm not sure how many of the Raccoon City street areas were the same as before, but from a different angle. Because a lot of what I saw looked completely different.
And according to the developers, the intention was to make it feel different from the RE2 environments. "The developers noted that the city setting allowed them to create more varied environments."

Even if there was a street in the original RE3 that was the same as in RE2, but from a different angle (still need to find verification on that), I'm not so sure they'll commonly just re-use that street from REmake 2. (Not that you spend much time in the streets in RE2 or REmake 2 anyway.)
Because in those cases the player was supposed to see an environment they'd never seen before.

Considering how much of REmake 2 takes place in areas you didn't see even in the original RE2, I wouldn't be surprised if they made such a street an entirely new one instead. Because there will already be some overlap in the game. Most notably part of the Police Station.
So I think they'll be mindful to keep that from getting out of hand.

They already have a lot of other assets to re-use to speed up production.

It depends on when they started. If they started after REmake 2, then even if it comes out at the end of 2020, that does seems quick to me for a game of this caliber, even all things considered.
For example, Persona 5 Royal came out 3 years after Persona 5. And that game is literally the same game as the original, but with extra content. And to render a character, object or background in P5 obviously takes a lot less effort than in a game like REmake that sports highly detailed textures.

If REmake 3 began development 2.5 years ago, then it makes me wonder what changed at Capcom around that time to make them comfortable making decisions like that again.