I think that misses the point of the memo. The 6600 was certainly something IBM had resources to design and market yet for some reason it couldn't.
In many ways, the 6600 would be unthinkable to IBM - it was a very limited machine, with 60-bit words and no character addressability, just ludicrously fast (and cool looking). The central processor was augmented by 12 peripheral processors that offloaded IO and other tasks from the CPU (not sure IBM did that, but this - channel processors and channel programs - is a pattern that was common on IBM mainframes at least after the 360).
It's very normal to slow down new model releases so they don't cannibalize too much of the sales of previous established lines. CDC was a very lean company, while IBM had a lot of different lines to protect from their own disruption.
It's always an important thing to remember it's better to develop the product that will kill your cash cow, because someone will, and you don't want it to be your competition.
A much greater omission was IBM's refusal to consider time-sharing, until it was too late, and then they made a total mess of it with TSS/360. (The 360/67 was a good machine, I have fond memories of it, but it needed a different OS, Michigan Terminal System in our case.) It took IBM a long time to understand the need for interactive computing.
I don’t remember much about time sharing being a thing at that time - batch processing made sense in both kinds of applications.
As for time-sharing,IBM explicitly ruled it out as a design objective for OS/360. Then MIT went shopping for a partner for Multics. IBM had nothing of interest for them, but GE agreed to design a virtual memory version of their 635, the 645. Suddenly, IBM realized that they were going to lose a market, so they rapidly added memory mapping to the 360/65, producing the Model 67. They also announced Time Sharing System/360, but the early versions were unusable (20 minutes to log in, for example), so a few folks at the University of Michigan whipped up an interim solution, the Michigan Terminal System, which worked fine, and was in service at various places from 1968 to the 1990s.
Although IBM produced various time-sharing systems, including Call/360, APL\360, the Time Sharing Option, and VM/CMS, they never really understood it, which is why a few underfunded folks at a university could produce something better than what they could produce with a professionally-managed team.
By contrast, DEC did get it in that era, which is why the PDP-10 did so well in university computer science departments.