The main difference between the comeback mechanics in SR and Dom is pretty simple, one is punishing you for winning, whereas the other is punishing you for making mistakes.
There's literally nothing in Sr that punishes you for winning. Any time you get an objective or kill, that's gold and map control for you. Comeback mechanics lie in the fact that Dragon/Baron and Towers can provide a couple thousand gold worth of stats when you fight at that location, so the game isn't over if you're say, 5000 gold behind, giving you time to capitalise on enemy mistakes. If you don't make mistakes, then you will simply win. But that isn't possible, even for some of the top teams in the game, which is where SR comeback mechanics lie - towers and barons are hard to secure with a marginal gold lead, which gives breathing room for the losing team to outplay the winning team.
In Dominion, comeback mechanics lie in the fact that Quests are unfair when they spawn on the Windmill, the losing team will have an advantage if they only need to cap the windmill. Respawn timers are pretty unfair, there's not really that much counterplay to them, in all honesty. Basically, if you're losing, you get comeback mechanics because you're playing bad.
Tl;dr, SR's comeback mechanics lie in the fact that games aren't immediately over when a gold advantage is gained, and there is so much room for one team to make an error even with a lead. However, these errors are 100% controllable from the team. In dominion, comeback mechanics simply exist because you're playing badly and are losing. The winning team on Dominion cannot stop this, only try to mitigate the impact.