This is true, up to a medium range freewheel, when the chain length in particular is near spot on.
In this state, the offset cage pivot does it's job in tracking a freewheel, even with the 42-52t in front.


As for that Skylark and Simplex Export 61, these are dual-sprung, so even better at remediating the effects of broader chainring size ranges, up to 36-52t, and still shifting well. No N.R. derailer (with it's fixed-position B-pivot) will handle that range well with larger-size freewheels like 28t or even 26t.

But note that the Skylark derailer offers no adjustment for balancing the A and B-pivot spring tensions, so it works best only with whatever sprocket sizes that the factory chose when deciding how to pre-set said pivot spring tensions. Simplex derailers, otoh, all have that external cage locknut and cage pivot hex socket to allow optimizing the pivot spring tension balance to one's choice of cogs.

A derailer doesn't have to be slant-parallelogram to track the freewheel's cone profile. All it takes is some cage-pivot offset, and from there a sprung upper pivot further allows compensation for changes in chainring size, for front shifting.
Shimano called this Servo-Pantograph, which competed with Suntour's slanted parallelogram. Shimano's design was borrowed from Simplex, but featured no adjustment to optimize for one's freewheel size selection.

From the beginning, Suntour's design featured B-pivot adjustment for use with various freewheel sizes, much as did Simplex's designs, only here it was at the "A" (cage) pivot.

In 1984, Suntour's patent had expired, so Shimano patented their own hybrid design that featured Suntour's slant-parallelogram together with "Servo-Panta" dual sprung pivots AND a convenient adjustment screw for B-tension. This is essentially the model for the last 20 years of Shimano's and Campagnolo's road derailers, except that Campagnolo variously used either the A or B-pivot location for the adjustment screw at different times.
While many of Suntour's Accushift indexing derailers featured a new B-pivot spring, this spring only served to pull the derailer rearward when a wheel was being removed, and did not float in Servo-Panta fashion while riding, it's position rather being fixed by the B-pivot ANGLE (not tension!) screw, just as on their older derailers.

Curiously enough, with a Suntour Accushift derailer's B-pivot angle screw removed, and with some internal up-tensioning of the B-pivot spring, these B-pivot-spring-equipped derailers operated in full Servo-Panta mode(!), with opposing A and B-pivot springs allowing dynamic float of the derailer body angle during gear shifting.

I thus modified a few of these Sprint and Superbe derailers to be more Shimano-like, and the results were fantastic. It definitely left me wondering: A); how Shimano's patent prevented Suntour from delivering their derailer's set up in this configuration, and B); whether Suntour perhaps intended for more-sophisticated (racing teams?) users to be able to set them up this way.
It seemed (and still seems) far too much of a coincidence to me, but I was connected to no team and had no insider information to rely on, just that dangerous combination of motivation and curiosity.
So, over time, I became proficient at disassembling the messy shimmed and sprung pivot out on the road, to achieve a final optimum adjustment setting for my "hills of L.A." gearing.
I even remember "sneaking in" one of these complex adjustments during another rider's tire change on a hilly training ride above Pasadena. Talk about "pit pressure", I only had a few minutes.

It was all worth it, right?