That might've been more a reflection on PLT than on Scheme48 (which also had some really smart people on it).

As some point, when I was writing a lot of basic ecosystem code that I tested on many Scheme implementations, PLT Scheme (including MzScheme, DrScheme, and a few other big pieces), by Matthias Felleisen and grad students at Rice, appeared to be getting more resources and making more progress than most.

So I moved to be PLT-first rather than portable-Scheme-first, and a bunch of other people did, too.

After Matthias moved to Northeastern, and students graduated on to their own well-deserved professorships and other roles, some of them continued to contribute to what was soon called Racket (rather than PLT Scheme). With Matthew Flatt still doing highly-skilled and highly-productive systems programming on the core.

Eventually, no matter how good their intentions and how solid their platform for production work, the research-programs-first mindset of Racket started to be a barrier to commercial uptake. They should've brought in at least one of the prolific non-professor Racketeers into the hooded circle of elders a lot sooner, and listened to that person.

One of the weaknesses of Racket for some purposes was lack of easy multi-core. The Racket "Places" concept (implementation?) didn't really solve it. You can work around it creatively, as I did for important production (e.g., the familiar Web interview load-balancing across application servers, and also offloading some tasks to distinct host processes on the same server), but using host multi-core more easily is much nicer.

As a language, I've used both Racket and CL professionally, and I prefer a certain style of Racket. But CL also has more than its share of top programmers, and CL also has some very powerful and solid tools, including strengths over Racket.