Hm, I think I see the thrust of your argument, G.W. Mumblefratz, you are correct on all counts. I've finished two gigantic galaxy conquest games to get the full experience; educational, but so time-consuming that I doubt I will do it again anytime soon.
Now to the original post: I had no interest in tiny or small galaxy games at first. That changed this past summer when there was a big kerfuffle about people's Metaverse scores dropping dramatically once they reached 16 games. I had just reached 15 games with my original character, but instead of whining on the forum, I just decided to start a new experimental character to see what I could do with the smaller settings. I'm still playing with that character, so for me the whole scoring problem was a good thing. I began to try out higher difficulty settings and different colonization strategies that have definitely improved my game.
The great thing about Tiny galaxies is that even I can finish a game in a couple of sittings, even with research speed set to normal. This size has a certain 'arena' feel to it, a kind of Thunderdrome 'two man enter, one man leave' competition. You have to be careful with your research strategy; pick your weapon and defense techs carefully, because you won't get time to build a second fleet - and ignore combat techs for other improvements at your peril. I never did manage to win this size game at Suicidal, though I intend to go back and try again some time.
After a few Tiny games, the Small galaxy size seems spacious (pun intended) in comparison. With fewer planets to micromanage than in a big galaxy, the game feels smoother than the larger sizes, but even with just a few opponents there is still a satisfactory amount of jockeying for position and politicking before the endgame wars commence. In my Small galaxy Thalan game, I lucked into two 26+ PQ planets in one star system and managed to get both to 100 billion population before the end of the game (using transports for some of that growth).
I've taken longer to play through my series of Medium galaxy games because they are more complex than the smaller ones, especially if you max out your number of opponents. You'll get one minor race if you don't turn them off, and I like to try to protect them as a side goal; that way, I still have a trading partner at the end. Even with research set to Very Fast, you still won't reach the end of the tech tree, so your research path still needs to be planned carefully.
Overall, the smaller galaxy sizes force you to do more with less, planning your research, building, and war fleets more carefully. You will micromanage less (a lot less) and spend less time watching your ships move across the map, but you can still field impressive military forces. The biggest benefit for me was that they have given me a chance to try new strategies and see the results fairly quickly, rather than playing a gigantic game for a month before deciding that my great new colonization ideas really sucked.
One piece of parting advice - slow AI ships have less distance to cover in smaller galaxies, so be really careful where you put your manufacturing capital, especially when you've built Eyes of the Universe and the Tir-Quan Training facility there...