Here is my stab:
Highest tier of ship is first. bb6 then 5 then 4... or cv6, 5 , 4
Alpha has highest level bb, bravo next 2, etc
Bravo has highest cv, alpha next 2. etc

BB6 seem to be ordered in range order KM, US, IJN, UK (I don't know how MN and SN fit in).
BB5 are split on BO and gunner level (probably support as well, but defiinately gunners)
Therefore it is not just the highest level BO that is highest in split.

A level 120 bb1 would be the highest bb1 so would not disadvantage a team, if anything it is probably better than a bb2 at level so is an advantage (possibly).
CV1-3 with 120 fp are a huge advantage to a team and can ruin balance, however the actual cv split is more of a dark art than bbs as you can get 5 vs 3 games.

Hope that helps.

As kila said.

First look at ship level, then at gunners level. Not sure for CV.

It does mean however that a lvl 120 gunned guam is classed lower than an at level scharnhorst however.

Team are splitted highest BB to A, 2nd and 3rd to B with strongest CV, 2nd and 3rd biggest cv to A.

One problem that sometimes arise is 2 nebby with a cv6 vs a kaiser with 2 lesser cv.

Rest get splitted after following a similar logic.

i think cv balance same as bb but started on bravo,

highest tier cv/higherst level player on same tier to bravo then alpha then bravo then alpha...

i find it always that cv6 landed on bravo if there is one in the room

The balance depends on the ship type but not sailors level, I think.