There is an item that allows users to gain another squad. That item is currently infinite, which is not good. At all. In fact, it is broken and bad for the game.

There should be a cap (maximum) for the amount of allowed squads per account.

As it is, the game is ruled by a single user. This is not a good thing. New users, or even returning users like myself, either do or will see this and not even want to bother with the game. If people don't even want to bother with it, it's only a matter of time before they quit the site entirely.

Valuable resources and schematics are only available by trading with the moon in the Battlefield. Having an infinite amount of squads means that one single user is able to monopolize these trades, which in turn means that no one else is able to get those things unless the person monopolizing the map decides to sell them. Even if the items do get sold, however, they can be sold for far more than they should be due to only one single person ever getting them.

Limiting the amount of squads a single person can have allows for other people to actually have a chance at getting the items that are only available in the Battlefield.

There is a very large need to limit the amount of squads a single person can have. A limit of five, so two extra squads by way of using the item, would be good. People would be able to look at the map and see spaces that they can try to get, which in turn would make people actually want to play.

The Battlefield has always been busy. It's not broken but supposed to be like that. Empty zones mostly appear when one squad kicks out another, and they are filled back pretty quickly. It doesn't matter how many players own these squads; while moving to the portal zone, you'll have to attack and defeat at least 4 of them, and if you're not using Squad Energy Packs, then your squad will be attacked while it rests. The Battlefield is not intended for new users. On the contrary, it's the highest level content the game has, requiring multiple thoroughly bred and trained pets.

There are no ultimate builds that can't be defeated. Plan your strategy. Choose a path in advance. Train your pets for research potential to get an advantage in the Mirror World. Analyze your potential opponents and create squads that can successfully counter their builds. Use a few squads at once either with duplicating or different builds depending on the situation. If you're aiming for a moon trade, you may just quickly move there and grab it while it's active. Some of them even go away unclaimed. Defending the key zones would be a bit harder, but protecting them for 1-2 cycles is doable as well. The most part of the reward comes from successful defence! 

The current Battlefield setup is far from the worst case scenario :) Nothing prevents you from becoming the third major Battlefield player if you're interested in this part of the game. The players who are currently active on the Battlefield dedicate a lot of time to it, but they don't do anything that can't be countered. If you don't like this part of the game, then your best choice would be trading Battlefield items from other players.

Two points that are false:

"requiring multiple thoroughly bred and trained pets"

Bred, yes, but it takes no training at all to have a pet with full potential. A newly bred pet that just barely grew to adulthood is capable of the exact same things as a level 50 pet that has been trained. The system only requires that stats reach 100 to unlock the skills, which is fully possible for a level 1 pet.

"The players who are currently active on the Battlefield dedicate a lot of time to it"

They do not. One of the only two people who own the entire map even state in their profile that they have almost no time at all to play. This game is so thoroughly restricted as to how much time you can put in that it requires absolutely no time at all to do anything. This is actually a point that drives me insane, due to my desire to actually play the game.

Spending maybe ten minutes on the game every eight or so hours is not spending much time at all - and that's all this game requires, really. I can guarantee you right now that I've more than likely spent more time trying to play in the last four days than anyone else on this site has played in two or three weeks time. If actually spending time on the site meant anything at all, I would already be at the very tip top of the food chain - a fact that I show on every single game I play that actually allows people to play for as long as they want.

Edit:

"it's the highest level content the game has"

This is also a false point. As stated above, even a level 1, newly matured creature is capable of the exact same things as a trained level 50; This is due to the fact that levels are completely and utterly ignored in the squad mechanic. Why it was designed to ignore actual effort of any kind, I will never understand. From a game perspective, it is broken/unbalanced to the extreme.

All games have endgame content - except this one. Even other games that focus on breeding while still being a game have endgame content. A perfect example of this is Final Fantasy VII for the Playstation. In that game, you can breed chocobos to get chocobos with higher stats as well as of other colors. The main purpose of this is for the racing, which is a mini game. The other colors each have a specialty in the actual game itself as well though, like the blue one allowing you to run across water. It is only by breeding the chocobos to get the best one that you can reach and obtain the best summon materia in the entire game. There is no other way to get it, aside from cheating.

Using the example of FFVII, the squad system on this site is as broken as cheating to get the best possible summon in the game. In FFVII you need to put actual work into what you're doing, whereas on this site there is no work needed to achieve anything at all. Yes, you need to strategize, but even the strategies are sorely lacking due to none of the creatures needing any actual work put into them for the squad to be at its best.

One more point crossed my mind while thinking over your ill thought out response, Angel:

"it's the highest level content the game has"

On top of the fact that level 1, newly matured creatures are capable of conquering the battlefield, there is the small fact that the "high level content" in this game is the event map for Explore; the Tundra. In the Battlefield, a squad full of level 1s can win it all if you have enough squads to throw everywhere - which is not effort in any shape way or form considering the fact that if you throw enough pencil at the wall, at least one will stick. In the Tundra, on the other hand, the Etalia are capable of being next to impossible to defeat even when using a Generation Power 3 Unicorn that has Magic Horn, Acute Eyesight, Quickmind, Agile Paws, Gracefulness and Regeneration. Almost perfect genes, as well as great stats, are still hard pressed to gain a victory on the higher level Tundra maps.

So unless the Tundra maps are broken, the event Explore maps are much, much higher level content than the Battlefield.