the people at Ansco would have likely figured that out
They were in the region of 10 years behind Kodak, going by some of the accounts that have been published. Kodak, Ilford etc had more significant in-house synthesis capacity (and interest), Agfa (and by extension, Ansco pre-1941) seemed rather reliant on being intimately linked to the German chemical industry. Post-1945, this changed, and most of the manufacturers in the west invested heavily in acquiring much more significant in-house capabilities.
Or maybe those Kodak people knew that glycin powder doesn't have a very long shelf life
Agfa/ Ansco managed to get the stuff to survive OK in 130 packaged in tins. If Glycin really made a difference, you can bet that Kodak would have found a way to make it cheaper and better protected from oxidation. They were very, very aware of all the cult chemicals that the garden shed formulators obsess over today (Glycin, Pyrogallol, Catechol, Amidol), and none of them were really up to the job that the fanciful home formulators of the very late 20th century imagined them to be. Kodak used them (pyrogallol and catechol) where they made a meaningfully functional difference (if something less toxic wouldn't do the job - and in some cases only persisted in doing so because the less toxic alternatives had not been commercialised due to ending basic research on the particular product line), and nowhere else. There were some much more complex customised organics that do seem to have been of interest, but overall, without massive expenditure on synthesis, the reality is that PQ can do a huge amount, it just requires a precision that may be lacking in home formulation, and in commercial terms, the developer had to appeal to the largest market possible - thus ratios that might be worth exploring for specific outcomes, might be dismissed as not commercially viable.
And, like with Henn's contemporaneous work at Eastman Kodak, who in formulating D-23/25/ Microdol had realised that there were no special/ toxic ingredients needed to make very fine grain development a safe reality, Levenson at al seem to have realised that there was no point in adding extraneous (and readily available) components whose functions merely equated to approx 50% greater quantity of HQ.
For the record, Levenson seems to have been the specialist in the characteristics of superadditivity (and where it fails).
D163 diluted for use is very similar to Dektol diluted for use except for the added hydroquinone. It was marketed for tropical use.
It is probable that it was formulated to replace supplies of Agfa/ Ansco 130 (pre-expropriation in 1941, where do you think the money was flowing to?) that was being used in the UK sphere of operations with tropical climates. Kodak Ltd later marketed it in preference to Dektol for a long time.
And it wasn't because of a lack of Glycin supply. May and Baker were using it in some of their developers (and they had given up on researching products using it by the mid 1950s too, going by the patent record).
The only real outcome that is important is that differences in the ratio of Metol/ Phenidones to source of semiquinones can make some degree of visually significant differences in print tone (but not enough for Eastman Kodak to have chosen to market D-163 - but they did produce a variety of other commercial developers than Dektol in the post WW2 era). Before making assumptions about similarity to Dektol, the M:Q ratio is what matters (which was one of the key insights of Levenson's work). That has essentially apparently long been understood by the mainstream of the industry and not adequately communicated outside. Possibly because it's not very marketable to the easily influenced if your developers don't contain anything other than Metol/ Phenidones and HQ/ HQMS/ Ascorbate.
For those who want to experiment, Levenson disclosed useful M:Q and P:Q ratios (including for Dimezone S) and their relevant pH ranges.