Problem with solo is that it's a total crapshoot what type of team you'll get. If there were a way to stay teamed up with certain players (or friend players while in multiplayer) after you left a lobby, it wouldn't be so bad. I usually don't remember to go through the list of people I played with to pick out the five or ten decent players I run in to after a couple hours of playing. They really should make it easier for player to hook up with each other in game. That's how I find a lot of friends in other multiplayer games: you just run in to a group of people you get on with and add each other on the spot.
Now, before I rain all over your parade, I'm a WildCard player which basically means I'm not a squads player, even though I like it because, *cough* I'm an S rank player, I hate turf war, and can't lose my rank in squad battles. I remember when I just connected to ranked battles the moment I hit level 10. I ditched turf war and haven't played it since. (7 months ago).
Now on to your idea, now looking at the whole one team forever deal, I guessed it was excellent, but a few things wrong with it.
1; Lag, matchups and more, It takes quite a while to take atleast 3 people from America, pair them up with 5 Japanese players, and then sorting out the teams, then keeping those direct teams, and doing the same thing again when more players shift in the circulation, there could also be a point where one team collects different players that are high ranked, now we're taking the squads idea now, then S+ ranked people could go against C- ranked people because there is now no such thing as C lobbies or S+ lobbies.
2. OverPowered teams, Now let's take the entire matchmaking concept of Splatfest, and then adding it to ranked and turf war... It's extremely possible for a few teams to build up super competitive people, and then those people just staying with that one team. Making even more random rage from random people.
3. Unneeded Tension (cnt no.2)
Let's name a squid person n0oB.
n0oB is flowing through the levels and finally gets to level 10 to where he can finally play ranked. n0oB is expecting a turf war with a little more difficulty. Until a team of C+s shows up and tension builds, n0oB is now tense and is ready for nothing. n0oB loses the battle.
n0oB is mad.