Don't think there such thing as it all down to budget and server host speed.
You get what you pay for.
All themes will run very quick perfect on the fast hosts.
People just seem to not want to pay for good fast hosts.
Speed from your host is an SEO factor these days now.
Trying to get a shitty host with the best fast themes is all old news google reads the host machine for speed stats these days, Google wants the best, shortcuts don't work any more.
All SEO experts know this.
Speed for SEO nearly 30% to 50% of indexing position know...
The quicker a page loads and the faster your links open pages and video and images are shown the more love google gives in indexing position.
But Google doesn't just use stats from the page opening, Google also uses the connection speed and host speed info. (( Google algo a different world know ))
You can use theme Astra on an old host computer, and it goes fast looks good, but that doesn't give you the push showing google the connection stats are shit it the theme keep you afloat.
Google no if that website grows the host can not handle high amounts of traffic for that website as opposed to a high-end setup.
Google hates websites down and that will cause it.
Only going by what I have bench tested