I still think the Aliens should always be biomechanical, to be honest, none of this diluting stuff.
To me, it makes sense that the alien Facehuggers would have no traits from any hosts, and be 'pure' Xenomorphs, otherwise over time the genepool would get so diluted from generations of hosts that the aliens might become weaker, not even the same species at all.
And I concede on the ADI point, they're not bad at what they do, they just don't know what makes the alien most effective.