Magatamas should be done psudo even, that is to say keep the level even overall. But as USUALLY you dont have all magatama at same level, you would like to have a focus on who gets the highest, ergo psudo. It's certainly true that, for example, if you have 4 lv 5 and 16 lv 4s, it is better to have the 4 lv 5 on one ninja that c*e it best than spread it even, but you should not have 9 lv 5, or even more extreme, 2 lv 6 and 3 lv 5s.

Simply speaking, because of the significant diminishing return of higher level magatama, for example take atk magatama 3 lv 4 contributes 213 attack while 1 lv 5 contributes 109 attack. Even if you could give the lv 5 to a ninja that gains 3 damage per attack per round on average, that's 327 damage per round. But if you give a 71 to that same ninja while giving 142 to another ninja that does only 1 damage per attack per round, you'd end at 71*3+142=355 damage per round. So depsite the magatama being "wasted" on a ninja that doesn't benefit from it nearly as much, even spread provide much more overall. As it were, atk/nin contributes differently to different ninja, but there is not a single ninja that does not benefit from them AT ALL.

An interesting thing to note, if anyone follow OP's advice, then they will be stronger than other players of same power, assume all else are equal. That's great, right? Well..... The thing is, it would make a person who COULD be, for example, 30k power that is "average" for their power become a 28k, and help that person "strong" for a 28k and maybe match up to a 29k.... So in reality it backfires. But hey, what do I know, there are people who enjoy being "strong for their level" and thus refuse to level (yes, I know there are sage brackets, so I only mean those people who do it even when their server doesn't have it or at a level where it doesn't matter), so maybe some people likes being "strong for their power"? Whoever knows