I don't think HP's RPN calculators were ever in competition with TI. The RPN calculators like the 12C are marketed to finance professionals, and TI has nothing like them. The HP graphing calculators like the 50g are infix (although there is a pretty good RPN app available).

Edit: I do see that HP made graphing calculators with native RPN in the late '80s, so perhaps they were pushing these for academic markets, although today they seem to be the provence of surveyors.

Random aside: I first learned RPN from my father, a budget analyst, and have used it ever since. RealCalc is an Android calculator app with an excellent RPN mode, if you're curious.