This is going to happen in Random Battles because there are 12 players per side. Even a brawling, armored battleship doesn't last long when pushing into the shellfire of 5+ enemies. There is going to be a period of time where long-range shells are exchanged until a few ships are sunk. When the numbers are no longer high enough to hold back a brawler, then they can go in secondaries blazing.
You see this already in the smaller 6v6 format of Ranked, or the 1-3 player format of Brawls. When there isn't a massive amount of damage to focus-fire down a brawling battleship, they will absolutely go in immediately and have a large effect while the enemy team tries to work them down without dying in the process.
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Random Battles can best be thought of as coming in 3 parts:
Early Game
Mid Game
Late Game
Early Game:
Players tend to split up to each flank. To be in the middle is to risk being shot from both sides, so fights break out for flanking positions. Since you can expect a roughly even distribution of 5-7 ships per flank, it's best to focus on TRADING. Trading is a process of trying to deal more damage to the enemy than you receive in turn. Dealing 10,000 damage to their team while your team only takes 5,000 is an example of a good trade. Repeated long enough, the enemy team will either lose ships or be forced to retreat.
Mid Game:
This starts after a few ships have been sunk. Usually both teams lose a few ships and start to look for what advantages have opened up. Successful trading will lead to kills and capture of strategic territory. If one team has lost both flanks, it can be extremely hard to come back. Sometimes the mid-game starts early when one side loses ships very quickly while the other team does not. The midgame could rapidly result in a route/blowout in those cases.
Late Game:
This starts after each side has lost half or more of their ships. Typically all ships have taken damage by this point in the game. Left with few resources, it's up to each player to make decisions that make their remaining HP matter the most. In the case of Brawling Ships that have saved the majority of their health, now they can push forward with the expectation of only a few enemies trying to wear them down. This allows them to forcibly take map position as the heavy armory and secondary pressure will drive back damage ships that cannot easily coordinate their fire.
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TLDR: Random Battles start with trading for a few minutes. As advantages/openings appear, then players get more aggressive and net kills. Try to save your health for brawling in the later half of the match when there are less enemies to focus you down.