That's a distributor problem, not a Harman problem. K400 in 120 should be around 75% of HP5+ price, and in 135/36 about 60% of HP5+.
No, but you are illustrating the point about baseline technical competence failures rather well, just not in the way you might want to.
Under your exposure conditions, Tri-X's useful shadow speed is about right for what you think it should look like. That's where most of your errors of comparison are coming from. Tri-X today is aimed to look like what people think Tri-X should look like when exposed at 400, HP5 (and HP5+) were intended to beat Tri-X for useful speed, thus when you use them under identical exposure conditions, you are effectively driving your exposure up the scale on HP5+ and making it look grainier and somewhat flatter in rendering. K400, because of side-effects of its lower cost construction, has a higher useful shadow speed than might be assumed, at a cost elsewhere (it's not as sharp, grainier than HP5+ etc and a noticeably lower image content capture/ transmission capacity). All things being equal, simply by adjusting exposures, you can make Tri-X and HP5+ look like what people assume/ claim the other must look like, but in absolute terms at larger scale enlargement or with high quality scanning, current Tri-X has slightly better granularity/ or at least 'cleaner' grain than HP5+, and HP5+ has slightly later highlight roll-off and a bit more of the grit (without as much of the image detail loss) that people used to associate with Tri-X. I use a lot of K400 in 120, but if you really think it's indistinguishable from current HP5+, then that's more about your equipment/ process/ practice limitations being inside the limits of K400, and not being able to address all of HP5+'s capacity.