Comment by pixelesque

They can be improvements, but you can do Data-Oriented Programming without ECS systems, i.e. Structure Of Arrays, which is what we often using in Rendering/Simulation for VFX for SIMD/GPU compute...

But similarly, ECSs can be slower, if they don't have some optimisations, i.e. spatial data structure lookups: just using a generic ECS "database" system without any first-class spatial knowledge / acceleration structure lookup ability, is likely going to be slower.