It's also that many Rails shops have performance problems: which isn't the same as saying "Rails is slow"!!. "Getting performance problems at some point" is almost a rite of passage in Rails; I'm certain every rails developer has pored over N+1 queries, caching, async jobs, race-conditions, gems and whatnot to keep the system running.
The only Rails projects that I worked on that never had performance problems are the ones that never reached any scale. All Rails projects that gained traction that I worked on, needed serious refactorings, partial rewrites, tuning and tweaking to keep 'em running. If only to tame the server-bills, but most of the times to just keep the servers up. Good news is that it's very doable to tune, tweak and optimize a Rails stack. But the bad news is that every "premature optimization is the root of all evil" project made a lot of choices back in the days that make this nessecary optimization today hard or impossible even.
What I'm trying to say is: Performance issues with Rails will sound very familiar to anyone who worked seriously with Rails. So it's not so strange that people reach for this conclusion if almost everyone in the community has some first-hand experience with this conclusion.
The only Rails projects that I worked on that never had performance problems are the ones that never reached any scale. All Rails projects that gained traction that I worked on, needed serious refactorings, partial rewrites, tuning and tweaking to keep 'em running. If only to tame the server-bills, but most of the times to just keep the servers up. Good news is that it's very doable to tune, tweak and optimize a Rails stack. But the bad news is that every "premature optimization is the root of all evil" project made a lot of choices back in the days that make this nessecary optimization today hard or impossible even.
What I'm trying to say is: Performance issues with Rails will sound very familiar to anyone who worked seriously with Rails. So it's not so strange that people reach for this conclusion if almost everyone in the community has some first-hand experience with this conclusion.