well..........Squads were formed on the basis of complementary fighting styles or skill sets. naruto's squad was formed por adding in Saske (to balance the immensely powerful but relatively unskilled Naruto) and Sakura was brought in because she was highly intelligent and there was a romantic triângulo angle in the trio that would encourage all of them to excel (in an attempt to gain the attention of the object of their affection). The 2:1 ratio was not uncommon, but was not universal, either. It's likely that the ratio of Ninja in leaf village (and possibly others) was close to 2:1, as well - if this is the case, it would nicely account for the large number of teams which respected the ratio.
the minimum number of people you need to create most flavors of dramatic conflicts - two people can shun one, one person can show they're stronger por defeating two, one person can be captured and two work to save them without forcing the show to resort to monologue
For example: In the Leaf Village, once a ninja initiate became able to take on missions, usually at the rank of Genin, they were assigned to a squad of three with a Jounin-level leader to provide guidance, coordination and experience to the other members of the team. Personalities would occasionally be considered for mission compatibility depending on the nature of the mission or the shinobi. In the event of a team needing backup, a segundo group of three Genin plus one Jounin would be assigned to support.
ANBU Black Ops traveled in groups of 4 to 8 members depending on their mission. This allowed for strength, reconnaissance and redundancy always ensuring a member of the team could return início with information gathered from their stealth operations. In such teams, the members were chosen, not for their sexual orientation but for the compatibility of their styles of fighting OR the compatibility of their techniques. This compatibility was looked at while they were still members of the Academy and promoted to ensure teamwork and coordination as they grew in power and skill. If you were a member of the Akatsuki, one of the show's major villain groups, you would be traveling in teams of two, chosen for jutsu compatibility. Personality was far less likely to be a factor in your relationship with your partner. Your partner would likely have shinobi jutsu techniques that were able to be utilized in a fashion that the two of you were a force to be reckoned with even against other elite shinobi.
Each of the trios we see from the Leaf Village tried to mix, reconnaissance, stealth, fighting prowess and healing ability in all of their groups. The Leaf village was also fortunate in having a relatively high number of elite and specialist ninja they could call upon. Other villages were not as fortunate, as many of their members where killed when the Great Beasts (Jinchuuriki) roamed the land before they were sealed away or destroyed. Later warfare would take a toll on many village shinobi reducing their numbers further.
but what about the jonin kakashi guy kerenai etc. I thought it was initially 3 but then I watched shippuden every team had 4 members example team guy had neji rock Lee ten ten and guy and at this point neji was a jonin so it was a team of 2 jonin and 2 chunin
also when naruto got back from training tsunade said their team is incomplete without a fourth so she assigned tomate to the squad because he can control the nine tails somewhat
like i said b4.........each team have a teacher.......a high class jonin to guide them.........this teacher is assighned when they r genin.......it doesnt matter if one of them became joinin in between bcz of his skill...........its like a class.........lots of students in it guided por a teacher.........what will they do if there was a child prodigy in it....who is topo, início class in all the sujects and curricular activities.........do u think the school management will make him their new teacher in that class instead of their real teacher bcz hes is prodigy...........????.......its the same in naruto.........its not just neji.........kakashi tooo became jounin at young age when obito and rin were still chunin guided por yellow flash...........and its not tomato.....its yamato.......by the time naruto got back,........in sasuke quest mission naruto and sakura were alonne and kakashi was injured.........soooo tsunade their hokage assigned yamato as their substitute teacher,,,,,,,,,,and put sai as their 3 replacement for sasuke.......and made the team trio with a new jounin teacher,........and if u didnt know.......naruto is still a genin......even now...when he is still hokage.........but everyone acknowlede his power they made him the new hokage........sooo in short. naruto shippuden animê other than akatsuki and anbu they have trio guided por a jounin teacher......i hope this cleared all ur doubts..........he he he he