95 for Smasha
78 for Let’s Poop

Lets Go: 83%
Smash Ultimate: 94%

PLG - 76%
Smash - 93%

Let's Go - 60%
Smash - 98%

Doubtful it gets nostalgia bonus, especially as there aren't so much genwunners and even less among reviewers. And more to it, nostalgia-fans probably hate Let's Go the most, as it diverts from the core of the series.

But on the other hand, there are more casual players. Some reviewers will like, that the series becomes more accessible. Heck, Pokemon Go got a 69 Meta, as Let's Go will not have many of the problems (the horrible connection problems for instance) and looks like an overall more polished experience, I can se it getting 10 points more. Some reviewers will say, this is the first Pokemon they can stand. Overall Pokemon will be much more polarising than Smash, while I can see much agreement in scores for Smash, the Pokemon Scores will wildly vary.

For some stuff I even hope this finds into the main series. That your partner Pokemon learns terrain moves and you have no longer the need for HM slaves is something I want in the main series.

For the question in the OP:

Smash: 95

Let's Go: 77

Smash - 94
Let's Go - 74

Pokemon Let's Go - 77
Smash Ultimate - 95

I think the changes in Let's Go will have a very negative impact on the score. Sun/Moon was 87, and US/UM was 84, I believe. Smash Ultimate is Smash 4 (92) with way more stuff, some smart engine tweaks and an actual single-player mode, whichI think will boost it overall.

Watch me be completely off and both get like a 87.

Pokémon Let's Go: 81
Super Smash Bros. Ultimate: 96

Pokémon will be criticised a lot specially due to Pokémon GO mechanics.
I think Smash will be one of the best fighting games ever. There's a lot of cool things in it, that's very nice.

Pokemon: 74
Smash: 92

Critics won't be nearly as turned off by Let's Go as some fans are. It's a pretty, more accessible version of gen. 1. I'd be very surprised if it gets lower than 75 and would actually predict low 80s.

Smash might start to suffer from franchise fatigue. I saw some outlets lower the score of Smash Wii U in 2014 because they had grown tired of the formula,and I suspect that trend might continue here even if has more content and more refined gameplay than previous versions. So low 90s to high 80s; I think a lot is riding on the spirits system really taking off since they're dropping trophies, which is a huge mistake in my opinion.