Isn't 4 the number of the devil or something like that in Japan ? 

Another great day for Black Ops 4!

Nope both are main games. Pokemon 2019 is just going to be the bigger project by Game Freak.

It's a main game but not a core game. It's Really weird. I wonder how consumers will respond to it

The number 4 sounds like the word for death not only in Japan but in China iirc

In terms of pre-orders it seems like it's being treated as some sort of middle ground between mainline and spinoff (gameplay is sort of like that as well).

Its doing significantly better than any of the spinoffs but significantly worse than the mainline titles.

But the pokemon company themselves classify Let's go as a main series title, regardless of the similarities to previous titles. however its more fair to compare its performance to remakes rather than generational entries.

I agree with you, but one point does distinguish it from Pokemon remakes in the past. It is using elements from different part of the franchise and combining them into one game. Like the switch it is essentially hybrid of Spinoff-mainline remake. 

At the most basic sense, it is a remake of Pokemon Yellow featuring Pokemon Go elements. 

And I thought this thread was spoiler-free! 

Wasn't there a thread about this discussion? Or probably someone start it in some other thread.