Welcome to AK, seannc.
I can confirm that your Hitachi was quite a good turntable. It cost less than the Technics SL-1200MkII (1979 Australian price AUD$377 versus Technics $419), and as some of that cost was for the fully automatic operation, it couldn’t be expected to match the fully manual Technics for performance.
The Dual 621 cost exactly the same price as the Technics, so was slightly more expensive than the HT-463. That may mean that the performance is slightly better for the Dual, but as I don’t have much info on that, it’s hard to say. The manufacturers’ specifications show the Hitachi rumble is ranked slightly better than the Dual, but that could just be Dual being more conservative. Wow and flutter can’t be compared, as they use different measurement standards. Both are fully automatic direct drive turntables with similar features. It may be that the Dual is slightly heavier as it has a wood base (hard to say, as they don't mention weight in the Dual owner's manual, so it may have sometimes been sold without a base), and so may resist acoustic feedback better, but in most respects they are probably fairly similar, being from (roughly) the same price range.
The Hitachi HT-463 was quite a decent performer, and in the reviews I have for each (by the same magazine) it actually matched the Technics SL-1200MkII for unweighted rumble, so it was pretty quiet. Other turntables with the same unweighted rumble result (measured by the same laboratory) included with direct drive the Akai AP-Q70C, Pioneer PL-400, Realistic Lab-500, Revox B795 and Technics SL-7, and with belt drive the Hitachi HT-320, Rega Planar 2 and Thorens TD-115. Of those, the only ones which were cheaper than the HT-463 were the Hitachi HT-320 and the Pioneer PL-400.
The only criticism that could be made of it, that was the same for many other cheaper model direct drive models of the time, is that it was relatively light (6.5kg). However, many other competitors such as the Technics SL-3200 (6.9kg) and JVC QL-A2 (6.5kg) were similar in weight.
Hitachi seem to be less well known these days as a hi-fi manufacturer, which is probably because they make lots of other stuff, and no longer make much (if any) hi-fi. They are a huge conglomerate operating in many different areas. Since I own a Hitachi cordless power drill, I can tell you they make good drills! The fact that their Japanese-market hi-fi was sold under the brand Lo-D rather than Hitachi also means it’s harder to find info on Japanese websites about Hitachi hi-fi. However, they weren’t alone in having different brand names around the world – witness Matsushita (Panasonic and Technics), Sharp (Optonica) and Toshiba (Aurex), among others that used a variety of brand names for their hi-fi.
All of the Hitachi turntables I have reviews for (which varied from an AUD$210 entry-level model up to a $500 one) were good performers, particularly for rumble (quietness) in relation to their price. If you want a copy of the HT-463 review, PM me your email address, and I’ll send it to you.