Joe, I think the manner of reasoning is about the well-being and ability to maintain the fish long-term. I understand this hobby is totally about the pleasure of the viewer (me), not the fish. If I wanted to stick a baby-nurse shark in a 45g, who is going to stop me?
Reasonably speaking a dwarf would be better suited to a smaller tank and if a non-dwarf is selected can be maintained for a similar amount of time if purchased in its youth (as it is interested to watch one mature) - but is not suggested.
No doubt the emperor perished of parasites or simply old age (fully grown, adult).
But on the matter of things, everyone can get what they want in their tank -- I'm just suggesting the pygme-fish for a greater possible success. Speaking specifically of mine and every other pygme I've observed, they are typically the most active of any other fish. Just IME
- not a scientific thing.
ps. To clear any confusion, pygme and dwarf are interchangeable.