I don't think they ever meant it's impossible to get there, just unnecessarily difficult (or expensive) due to a regulation that is bring unnecessary hassle (which is exactly what you are describing, but, somehow, using a tone that it's something smooth).

They don't let you check bags right before the plane takes off - AFAIK it's either 30 minutes or an hour before depending on what airline and airport[0] you change at. So a 2 hour layover "to be safe" would at best give you a grand total of 15 minutes to get all the way back to departures, recheck your bags, go through security, the immigration checkpoint, get to your new gate, etc.

If there's any delay, you miss your next flight, and the airline will not rebook you because your layover's a self-connection, not an actually ticketed thing. So your Guam trip just became a Japan trip.

3 hours would actually have some safety margin in it for short delays. Personally I don't get how people manage really short connections, and I hear plenty of people getting screwed over because of them.

Also, I'm not entirely sure how this works with immigration. The visitor form for Japan asks you about your hotel you plan to stay at - which you won't have since you aren't intending this to become a Japan trip. I have no clue if the immigration officer actually checks that field or if it's purely just for keeping records on tourists.

[0] I heard an hour at LAX. This is the same airport that universally refuses to store luggage overnight - a fact that even people in the airport industry don't seem to understand - so perhaps this is just a rule specific to that tire fire of an airport.

A backpack and a production crew :)

You don’t need to go through immigration at Narita if you are just transferring planes at the airport.

You don't get a transfer if you've bought two separate flights. You have to pick up your luggage and put it on the next flight.

If the airlines have agreements, you can often get your luggage automatically routed to your next flight. I used to do that between Alaska Airlines and Hainan. Not sure if you can get that done in Tokyo, but it wouldn’t surprise me if it were actually possible.