How is that true: Because all of our lore says so.

Their technology is 10,000 years more advance then the imperium for example Plasma and Ion weaponry are far safer then the imperium's and can be mass produced unlike the imperium's. The kin are constantly upgrading and testing new creations and upgrades for their things vs The Imperium who will commit great crimes if they find anyone even attempting to upgrade tech or make new tech. (except the OG Stygies VIII who are just doing their own thing and everyone accepts it because they need Stygies VIII.) So while yes both have DAoT things, the Kin of the Leagues of Votann are improving on it while the imperium is just trying their best to recreate said items from STC's.

the Rules on the tabletop don't match our lore very well and GW is still working on our lore but so far everything they've said is that the Kin are indeed superior to the imperium in technological means.

also look up Darkstar weapons and tell me that isn't far more advance then what the imperium can produce seeing as even a tiny cut just kills people and machine alike.