Interesting results, although the numbers seem on the low side to me. It did prompt me to get out my pull meter, though, and I tested several locos.
A brass Mogul (ex-B&M B-15) showed at 2.4oz., as did my Bachmann 4-6-0s and a Proto USRA 0-8-0.
Slightly better was a brass 0-6-0 at 2.8oz, and an Athearn Mikado at 2.9oz. My Bachmann 2-8-0s came in at 4.4oz., closely followed by a Bachmann USRA Light Mountain with 4.5oz.
All of these locos have been modified with additional weight.
While I don't normally run diesels, I did test a few. An unmodified Atlas S-2 came in at 3.1oz., while a re-motored and ballasted Athearn Blue Box geep showed 5.1oz. and a ballasted Model Power FA-2, with its original motor, hit 5.4oz.
A bit of a surprise was the one diesel which I do run often, a Rivarossi combine which I've made into a doodlebug. It showed a pulling force of 4.4oz., not bad for a can motor running a single truck out of an Athearn Blue Box F-unit.
Pretty-well all of these, the switchers and doodlebug excepted, normally run with another locomotive due to the numerous grades and curves.
Wayne