Let's Go Eevee/Pikachu is a remake of red/blue
This isn't restricted to the Let's Go series, but all modern Pokemon games (starting with X/Y) are absurdly easy in comparison to the originals; don't expect that you'll ever be in any danger of losing a battle.
(Also, Pikachu/Eevee are not remakes of Red/Blue - they're remakes of Yellow. But that's a small difference.)
If what you want is online multiplayer pokemon battles with just the first 151 pokemon eligible, I'd probably go for Sword/Shield and try to round up support on Smogon for your "only gen I pokemon" format. If you want to replay Yellow, then Let's Go is what you want.
Oh man, that’s tragic :’( I knew there had to be a catch. I genuinely don’t understand why they wouldn’t just remake the originals! Surely I’m not the only one in my generation with nostalgia and a professional salary to spend on video games.
That all sounds like singleplayer stuff.
The change in difficulty level is, in my opinion, bad. What happened is that pokemon now earn half of an opponent's experience value just by being on your team during the battle, and full value if they participate. (Catching a pokemon counts as defeating them.) The older system was that the opponent's experience value was divided evenly among participants while spectators got nothing. So for a battle in which two of your pokemon participate in defeating an enemy pokemon worth 400 experience:
- In generations I through V, your two participating pokemon would earn 200 experience each, for a total of 400 experience.
- In generations VI forward, your two participating pokemon would earn 400 experience each, and your other four pokemon would earn 200 experience each, for a total of 1600 experience.
But this 300% increase in experience earned by your team (250% in the likely case where you only have one participant per enemy) was not accompanied by any increase in enemy levels or in experience required for you to level up, or by a decrease in enemy experience values. You just earn ludicrous amounts of experience and dramatically overlevel everything prior to the elite four, and there's nothing you can do about it. It is not possible for a pokemon on your team to fall behind in levels even if you never use it at all.
As a separate concern, specific battles that were viewed as challenging in the original games tend to be nerfed in the remakes; the notable ones are Whitney in Gold/Silver and Cynthia in Diamond/Pearl.
My point still stands about the tile-for-tile remake though. I thoroughly enjoyed them. But then I wasn't at all bothered about fighting wild pokemon, and honestly the original games had virtually zero difficulty for me anyway. Just waste a bunch of time fighting wild pokemon to boost your stats every so often, then carry on winning at everything. There are reasons to try things like that in the new game - catching the same pokemon multiple times increases the chances of shinies appearing, and pokemon with better stats.
Each to their own, but for me it was a good nostalgia kick, and I'm not going to get upset if some of the mechanics have changed a bit.