Do you have some specific examples of games where this happens? Like links to your match history?
I dug through your match history and was looking at http://matchhistory.na.leagueoflegends.com/en/#match-details/NA1/1850233880/45771775?tab=builds in particular. Sadly, I don't get a really good picture just looking of the match history since I don't see many things that lead up to kills and objectives. So take what I say as a grain of salt.
Dragons and in general objectives. You guys were having a decent early game, despite getting aced and I don't know if everyone got demoralized over it, but it just got sloppy after that. A lot of objectives were just given away. It's not always ideal to fight the team at an objective vs say pushing a tower or two. Barely any headway was made after that.
Outside of that and not that you had control over it, your Katarina either wanted to go ham all the time or got caught out all the time. :c
It shows you as a team did more damage to them, but they must have focused the damage vs wide spread damage. The only thing I can think of is when you are that fed, play confident, but not blindly ignorant. If you are pushed up and don't have a tower behind you and no wards, fall back. Don't let yourself get caught out. And don't go balls deep for the squishy back line, hit what you can but stay out of range if your an adc or ap mage. If you're an assassin, by all means go for the back line safely. If support, top or jungler make sure the carries are ok and either peel for them or go ham for the back line.
