I never found that those two have a big difference except that healing items are less effective.
That says more about your (high) level of skill and native talent than about the ITYTD vs. HNTR difficulty gap.
On HNTR the monsters that
can miss do so less often, small healing items give half as much healing, armour shards restore half as much armour, acid and lava do twice as much damage, you find half as much randomly-generated ammo (not a
huge concern, admittedly, given that the ammo types you most often care about are routinely dropped by one flavour or another of former) and buffs last half as long.
IMO, a melee win on ITYTD is easier than an Ammochain win on HNTR. (Even a
knives win on ITYTD might be easier.)