Complex sentence: Others believed adding a significant amount of speed or firepower--something one would expect with an increase in tonnage--would require many more than 18,000 tons, and argued that the increase in size would buy nothing more than an increased target profile.
Split into simpler sentences: Others believed adding a significant amount of speed or firepower--something one would expect with an increase in tonnage--would require a much larger size than 18,000 tons. They argued that the increase in size would accordingly buy nothing more than an increased target profile.