Quirrell's tale of "I played a hero, but it didn't get me political power" doesn't hold up. The "lonely superhero" is just as much a mere storytelling convention as the "zero-casualties superhero". Either Quirrell is leaving something out, or the author is ignoring real-world politics for storytelling convenience.

In real life, successfully fighting societally recognized enemies gets you all kinds of political opportunity. Look at American Presidents Eisenhower, Grant, Taylor, Jackson, Harrison, and Washington. This is true in nondemocracies too: consider the Duke of Wellington, the Duke of Marlborough, or Sir Francis Drake.

What gets you loneliness and isolation is being a pioneer.

In real life, heroes go unrewarded exactly and only when their enemies aren't yet regarded as enemies by the rest of society.

The socially isolating thing isn't fighting Nazis when you're an American, it's fighting Nazis when you're a German. Being a reformer is isolating.

"The lonely superhero" is just as much a mere literary convention as "the zero-casualties superhero".

Of course, "the lonely superhero" reflects an underlying truth. The real bravery we could use more of from people is the bravery to give up status.

So the deeds we see Batman and Superman perform are mere stand-ins for socially brave deeds that make less good stories but matter far more: the scientist defending an unpopular hypothesis, the leader admitting to his followers he doesn't have an answer, the skilled and intelligent person who chooses to work on something that matters instead of something that makes the most money. Those are the real heroes we need, and they really are lonely.

So just as "the zero-casualties superhero" is a literary figure for "we need people who'll take risks for others", the "the lonely superhero" is a literary figure for "we need people who are willing to be mocked for doing what's right".

But within the context of the story, Quirrell's "I fought the villain but got no respect" is nonsense. Humans don't work that way. We have to assume Quirrell is leaving something out.

Did Dumbledore see through him and undermine him politically at every turn?

Alternatively, perhaps Quirrellmort is as bad at mass politics as he is good at individual violence? There's evidence he's got no clue how to handle 'inspiration' as a motive, though he gets 'greed' and 'fear' just fine.