Better quality is a better answer. AWS charges a big premium for Elasticsearch and I don't think they'd drop their prices to try to squeeze Elastic - for one, it would be unlikely to even work - but even so it's always best to differentiate on being the better quality/"value" than the lowest cost.

Having used AWS Elasticsearch, it has a lot of deep problems with it in its current state so Elastic can compete on value just fine.

In other news, I think the Elastic licensing change beyond being ethically a dick move (legally it's their right), is just horrible business strategy. I said on this site several days ago that Amazon was just going to make an Apache 2.0 fork and keep chugging along, and that's exactly what we're seeing.