This is true to some extent. Yes, in terms of "Jack Daniels calculator" or "equivalent performance calculator", 800m specialists obviously won't and shouldn't be anywhere near the equivalent age-graded 10k time. However, they DO need appropriate stamina to run well over the 800m.
In your case, if you truly had 46s 400m speed (or lets say 47 flat), speed likely wasn't the limiter. There are people running 49 flat who can run 1:46 (often mile specialists), and someone like Symmonds ran 1:42 based off a 47.4 400m PR. His 10k was always very good, he ran high mileage (~70) AND did aerobic cross-training in the pool. I guess his 10k was around 29:30, similar to the ability of Lewandowski (who also "only" has 46s 400m speed, but did 100+ mpw to get the stamina required for racing 800m).
Tinman himself once made this table of where he think an 800m runners stamina should be (and if it's not, he would prescribe more CV intervals and tempos):
800m 10,000m
1:42.0 29:07
1:45.0 29:59
1:48.0 30:50
1:51.0 31:41
1:54.0 32:33
1:57.0 33:24
2:00.0 34:16
2:03.0 35:07