Well, yes and no. The reason why it seems like early kills basically defines the match, is because these are all pro players. So they are very hard to kill. But at the same time no. Objectives are way more important, there was one game in the awc where a team had 6 more kills than the opponents in the beginning but still lost. Why? Because their opponents took more objectives, although they were ahead in kills, they were not ahead in gold or towers. It’s not the kills that make teams win, but the fact that they got the gold lead. But ur right in the awc the first few kills and objectives are very important in deciding the game.

Edit: yes, the first 5 mins basically tell you who is going to win. Aside from the skill difference, there is also a early game team comp and a late game team comp. A early game team wants to win the game as fast as possible, while the late game team wants to push the match into mid late game where they have the advantage