Here's my reasoning for wanting the game to be a few years down the line. 

1. I'm told the Gamecube ran into serious problems when after 18 months it got a lot of major games within the first two years (Melee, Wind Waker, Animal Crossing, Sunshine, Prime, etc). Having a definiate title known to the future helps aleviate this with the Switch already having the equivilent of Wind Waker and Sunshine out in year 1. 
2. Metroid is a critical darling but not always the sales best. It would do itself good to have as many people around as possible when it releases. 
3.  With Metroid not being so immediate it requires Nintendo to be creative with filling in until it comes around. Be it a Kid Icarus Uprising esc title, a co-op like X Warriors, or a Arms/Splatoon title it means they can't use Metroid as a mean all end all and have to try something else in the meantime. 

Given how vague the announcement was, I wouldn't be surprised if it was a 2019 or 2020 title.

No, it's not wrong. Tell let anyone tell you otherwise

Nope but I can't say I am hyped for a logo, but I guess people can be hyped for really long times. The last of us 2 was showed early and I have little hype for it, but that will come closer to release. Sometimes it's just nice to have something to look forward too. But I feel like many aRe making this a way bigger deal than it should be.

Not expecting it till Q2-Q3 of 2019 at the earliest.

I don't see why anyone would expect it before then...
I fully expect Xenoblade 2 to get delayed (at least in the West), and I won't even be disappointed, but I guess that's a different topic...

I wouldn't have my hopes for it being released before then. People expecting it to come out any sooner should prepare for disapointment.

I think earliest you ll see it is 2020..

It's not wrong to want the Switch to have a consistent flow of quality titles throughout its lifespan. Hopefully it can achieve that, regardless of when MP4 specifically comes out.

It's wrong. The main argument against it is: if they delay the title so substantially it means it is in development hell and might also turn out bad. Sure, rushed titles are missing polish. But a delay of a year or more is sign of something went really wrong.

For your point:

1. No. If a title is ready early on it means the team is free to develop the next. If development drags out it means fewer titles overall. Which is bad for every system.

2. Well, there is a point to it. But usually install base only helps you so much. A title like Mario Kart can in itself sell with owners of the system that look for some title to pick up. More niche games like Metroid are bought by people who want that title. It means it can drive sales of the system in that niche, but also that few putside of that niche are interested to pick up the title, even given the opportunity. By 2018 Switch should be sold to most enthusiast and the ones waiting for Metroid will pick it up at that point. So I doubt the game will be impacted severely. If it would've been a launch title your reasoning might be more fitting, but by 2018 the system should be much more established.

3. Or they could be afterwards. It doesn't really matter. But again: slower development = fewer titles. Including fewer creative titles.