My take on what can be changed for FFXIV

[Absimiliard]

I have noticed though my damage numbers are at my highest whenever a boss battle starts, but then it peters out for the rest of the battle.

That would be the two-minute meta at work. Your team goes in hot, dumps everything they've got, then spends the next two minutes slapping the boss with pool noodles. The average player won't properly manage their cooldowns and/or rotation, so the next burst window (if your target even lives long enough for you to see it) likely isn't going to be as robust as the first due to drift. There's also the matter of bosses being designed to choose violence especially hard during the period SE estimates your group's window will fall, which even further lowers your numbers.

The two-minute meta is one of very few things all corners of the community seem unified in their dislike of.