I find that adding heavy tanks to infantry can still be viable in a few, limited, scenarios. The major nations all start spamming AT support fairly early on, so you are correct in that it isn't useful in most cases. But I rarely (if ever) see China use AT, so much to the point that light tanks are effective against them well into the 1940s (why is Japan fighting China in the 1940s? Because they spent the late 30s knocking the US out of the game first). Japan can gain a real benefit from using heavy tanks in Infantry divisions against China. India can benefit from the tactic when holding the line against Japan. Japan doesn't prioritize AT because their first opponent is China, and China doesn't field tanks in any real quantity. So by the time Japan starts putting AT support in their divisions, their research has likely lagged behind where it should be. They might be putting AT support in their divisions, but it is likely to be 1936 AT while an India player could be fielding 1940 heavy tanks. Use army XP to boost your tank's armor rating and you can widen the gap between Japanese AT piercing and Indian armor. Of course, those same Indian Inf + Heavy tank divisions would be useless against Germany (or even the USSR if you end up fighting them for some reason).
Also, if you are playing as a minor nation, and focusing on smacking down other minor nations, it would still be effective (as most minors struggle to build enough MIC to fill out support companies) if not for the fact that it is a rare minor indeed that A) gets a large enough MIC base to afford putting tanks in infantry divisions B) has the steel and chromium resources to afford it, and C) isn't involved in a war against a major nation which would just invalidate the tactic through AT support.
But yes, the tactic is mostly useless in the current build of the game. The AI does a better job of using AT and most human players know to include AT in multiplayer, so it is no longer the instant-win button it used to be.
TL;DR Reman, you are right. The tactic is garbage in 92% of scenarios. But for the remaining 8%, it can still work.