I feel like you're deluding yourself, season 1 was probably the time when the game was most heavily balanced in favor of offense.
Think of it this way. Everybody is godmode. Then which team wins? Whichever one can siege harder. Nobody will die except in a minute long full on engage, and even then the most eventful thing likely to happen is Banshee's gets popped a bunch. The game turns into a grindfest where everybody knows who has won already, it's just an hour long formality as your inhibitor turrets lose 100 every wave, and 25 fucking creep waves later you maybe finally get a fight, but nobody dies and it is a sound defeat for your team and they take an inhib. The next 5 minutes are the enemy team cautiously approaching your nexus turrets, getting 1 or 2 potshots off at the turrets, maybe destroying 1 turret before having to kill the inhibitor again, eventually after far too long finally managing to kill your nexus. It doesn't matter if you get the jump on them and start a fight heavily in your favor because they can just disengage and go heal and continue sieging, and even if you kill them, what are you going to do? You maybe take an inhib and baron before they respawn, they stall out the game a bit then resume their previous dominance because it's purely a matter of teamcomp and who can waveclear better at that point.
Now think of the flip side. Everybody dies in 1 hit. Suddenly the game gets a lot more interesting. Now there's actual strategy in starting a fight, because whoever can land the first attack gets a huge advantage in killing someone, and the opposing team has the option of either running away and trying to stall until they have a 5th person and lose an objective or two, or they can try to fight down a man and short of something really, really strong like Fiddles+Kennen probably get destroyed. And it doesn't matter that they lost whatever objective, because the team that's down can still kill the enemy team and do something. That's the important part. If you can't kill the stronger team then the game is already lost and the rest is a formality, full stop. Swingy games come from everybody being able to kill eachother, not from nobody dying.