Two assumptions need to be accepted before starting my argument.
First: The greater an impact a players input has on a game, the more fun the game will. An important distinction needs to be made here between addicting and fun. Gambling is addicting, and this addictive quality is why people continue to do it.
Second: If two weapons, weapon A and weapon B, function differently, there are two possible outcomes. One, weapon A and B are each better than each other in certain situations(rock,paper, scissors), or weapon A is always better(DMR pre-Turbo update).
When designing a loadout sandbox, the idea is to have weapon choice matter, and not be functional reskins. The only way to do this is to have weapons function differently. When weapons function differently we run into my second assumption and end up with rock paper scissors or one weapon that is superior to all other choices. Let us start with a basic rock, paper, scissor style balancing. Weapon A’s rounds travel 15 meters then disappear, while Weapon B’s round do not appear until they are 15m away from the barrel. Both weapons are one shot kill. With this type of balance if weapon A runs into weapon B outside of its effective range, Weapon will always lose irrespective of the player input of Weapon A. Which according to my first assumption means this game is less fun than it could be. Now lets us use a real example with Halo 4’s carbine and BR, two weapons which are relatively well balanced. According to my second assumption, either one weapon is always better or each are better in different situations. The situation in which the BR will always beat the carbine still exists even if it is rather rare. In this situation both players are equally skilled. If player A with a BR and player B with a carbine both round a corner with a sliver of shield and see each other simultaneously, player A with the BR will always win. The input of player B doesn’t matter at this point and goes against my first assumption. The rarer the situation becomes in which one weapon trumps another, the closer to being a reskin these weapons become.
The problem of balancing load out choices becomes even harder when you allow weapons with different intended ranges into the equation. Let us use the AR and the BR to illustrate this point. We can design the AR to always win up to a certain distance, and the BR to always win outside of that distance, but this is rock, paper, scissors design which trivializes player input. If we make their effective ranges equal one becomes a universally better weapon which defeats the purpose of a load out. If both weapons have the same kill time and same effective range, the AR becomes the better weapon because of a smaller difference between optimal and average kill times than the BRs average and optimal. If we make the BR have a faster kill time, the AR becomes a useless weapon. If we balance the weapons average kill times, the optimal kill time of a BR will always be higher that the optimal kill time of the AR, again making the BR universally better.
The more weapons that are added to the mix the harder it becomes to create infrequent occurrences of rock, paper, scissors, without making one weapon universally better.
If we want to go the route of rock, paper, scissors we need defined classes, if we want to stay a non-class shooter we need to have identical starts( or at least very infrequent occurrences of rock, paper, scissors).