Some argue(d) that their function was to stiffen the iron, there were no thin irons when the chip breaker were invented. In this picture a typical wooden plane tapered iron (right, approx 3/16" / 5mm) next to a metal bench plane iron. The chip breaker was not used to stiffen it.
Here are a couple of paragraphs from Leonard Bailey's patent for his design of the cap iron:
Bailey's Patent Cap Iron.png
The full copy can be found at > https://pdfpiw.uspto.gov/.piw?PageNu...&docid=0072443
Some of the early cap irons sat flat on the blade iron and did not have the tensioning effect of the Bailey cap iron.
If earlier cap irons were used to control tear out, then Bailey needed a different reason to patent the set up of his thinner blade and cap iron.
jtk
"A pessimist sees the difficulty in every opportunity; an optimist sees the opportunity in every difficulty."
- Sir Winston Churchill (1874-1965)