OLTP != OLAP, and the sooner database vendors learn to stay in their lane and focus on one use case, the better.
I mean on the fundamentals Heatwave adds a giant memory cache / query engine in front. That alone makes it faster than anything disk based.
As to Redshift, yes, they claim it's faster than Redshift too by quite a bit.
(I use claim as it's against the ToS to benchmark it independently)
Being in-memory does not make OLAP databases faster. And typically, "in-memory" is a disadvantage and a limiting factor in OLAP database architecture.
I have a presentation on this topic: https://presentations.clickhouse.com/meetup53/optimizations/
It is similar to how frequently someone says "lock-free" to highlight imaginary performance advantages. If someone says a database engine is fast because it is in-memory and lock-free, it smells wrong.