We're not playing this like the HL2 videogame, we're playing as characters in the Half-Life 2 universe bar the features that were present in the game so that the player could win it. (e.g. Enemies being weak, you being overpowered.) I'd use the word "realistically", but I understand the flags that would arise if I were to use that word.
If you didn't want to play as an underpowered, beaten down and weak resistance that is constantly under the threat of being squashed by the Union's boot, then you shouldn't have made a resistance character. Similar to if you didn't want to play as a cog in a huge war machine that has strict rules and requires you to have your humanity stripped away, you shouldn't have made a Combine character.
Simple as.