One problem with regards to heavyweight torpedo (HWT) on submarines would be their effective strike ranges versus those of the AShMs...
Correction version below - Dear mods, please delete my previous post on the YJ-15 above.
One problem with regards to heavyweight torpedo (HWT) on submarines would be their effective strike ranges versus those of the AShMs.
The HWTs of today don't reach triple digits of kilometers of effective strike ranges, given how large their sizes would need to get in order to meet those requirements (or having to resort to nuclear propulsion, which introduces a whole lot of new problems to deal with).
The
YJ-19 AShMs, assuming to have similar effective strike ranges as the YJ-18 AShMs which it is meant to succeed on submarines (~500-600 kilometers) far outrange the HWTs that all SSNs (and SSKs) field. In addition, AShMs should offer the SSNs much greater operational flexibility in standoff strikes against enemy warships + Better chances at evading enemy ASW efforts than HWTs.
Sure, the
YJ-19 has smaller warheads than HWTs due to strict size limitations. However, achieving a mission-kill against an enemy surface combatant (e.g. destroying the main radar and sensor systems, or blowing up the CIC) without actually sinking it would still constitute a "kill" in the overall battlefield nonetheless, as said enemy surface combatant would be left blind and unable to contribute to the enemy's war effort in a warzone without getting drydocked for repairs, if not leaving said enemy warships more vulnerable to subsequent allied attack attempts.
As for HWTs - I would expect their main use on SSNs (and SSKs too) in the future would become more relegated to strikes against targets of opportunity during combat patrol or ambush missions around maritime chokepoints, with countering enemy submarines in self-defense being another key use.