Law literally saved Luffy in Marineford
Law and Kidd have had major impact to the story. Beating a yonko is more impactful to the world than all of what the SHs accomplished combined in pre-ts. It made every other major player move and shifted the power dynamic.
Law had important background narrative just like the Rocky Port Incident. Became a warlord, half responsible for the defeat of Joker - an underground mafia boss in the new world.
Law is also a D clan member whom will have a key role in the final war, like what are we talking about here
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Law was a major player all post-ts long, basically the deuteragonist. He‘s basically had more impact to the story than most top-tiers sitting on their ass.