I think many people don't run 5/3 because they don't understand the math, or they try 5/3 and get mad when they get 3/1 splits without realizing that you get pretty much the same number of 3/1 splits running 4/4. You also have to account for that some of the 3/1 splits you would get with a 4/4 now become 4/0 hands, which are very high quality hands (imagine if you could run mono with just 5 characters).
In a 4/4 preset, in your 3/1 splits, each of your 8 characters have an equal chance of being the character without the bonus. In a 5/3 preset, in your 3/1 splits, 93% of the time the character without the bonus is one of the 3 characters in your diminished 1/2. So let's say I was making a 5/3 Piranas
. I'd rather have 93% chance that the character without bonus is Cyb Lhia
, T Gaank
, than an equal chance that Tyd
, Dalhia or Tula
are left without a bonus.
If you don't believe that 5/3 gets about the same 3/1 splits as 4/4, you can do the math or you can test it out yourself.