If it is equal to or better than the other options, it will be played without the need to impose a mandatory minimum. Therefore the army building is flawled as a concept, from game design point of view.
It would be like saying in Magic The Gathering, that any deck must have a minimum of 15 lands. It is something that 99% of the people are going to do anyway, and as such it is an "empty" restriction, that only kills that 1% of variability (that 1% is not OP because if it were OP everyone would play it)
The opposite also stands true: Making a "max N" cap of something that is already subpar, is totally redundant and empty, because nobody will play it anyway, let alone max it out (Example, max 2 Giants in WHF:8th Orcs and Goblins book).
Note though, that "better" doesn't always mean just better stats or cheaper cost. Sometimes some armies have "better" special or rare in a unit that can fill a role very needed in the army. For example in Dwarf's case, the Copters give the army a mobility that they lack elsehow and thus they are very valuable.
TL, DR: To put it simply: If both were the same, why would anyone use the Special Honor Guard instead of the Core Veterans?
ETC 2013 FAQ, Referee
ETC 2014 FAQ, AR, Spanish Captain
ETC 2015 Chairman
ETC 2016 Chairman, Referee
ETC 2017 Referee