It matters for the playstyle and you seemed to be alluding that it's generally over the top and I don't think it is on hard or above for new players.It doesn't matter if the player knows the ins and outs, what matters is what you're able to do in the game. The typical player will likely play on an easy difficulty setting and blast his way through the game.
Ellie taking out a group of enemies isn't inherently over the top, if she does it with stealth and a lot of skill then it can be done believably, you seem to imply it's over the top in all situations.The only realism is the elements OUTSIDE of the gameplay. The over-the-top element is what you're able to do and how one player can take down a group of enemies alone.
Usually the designers introduce some mechanics or situations into the fight to explain the boss not going down as easily as the average enemy, otherwise it would be off-putting.The typical gamer likes that type of action and that's how the gameplay is designed.
The average player can understand the difference. Somehow the player can take down groups of enemies but they struggle to take down a main character during a boss fight.