"Bigness" is such a subjective concept having nothing to do with current league position and something that fans will always argue about. On your bandings we're probably in the Sub Wannabee category as you say "no recent history of extravagant failure" for a wannabee club and our current predicament might be described as such.
However, I would argue that there are some clubs on the wannabee list that I'd argue we'd be at least on a par with in terms of "bigness" (e.g. Carlisle, Millwall, Huddersfield, Port Vale even Wigan may be in the Premier League but I'd argue they're relatively a smallish club).
For League 2 we're a "big" club, in the top 5 for "bigness". In League 1 we'd be top half, but when we were in the Championship, I always felt we had a small club feel about us, even when we finished in the top half. Like I said, this has nothing to do with league position. I've always thought our natural position is top half Div 3(in old money - League 1 to the kids), maybe bottom half Div 2 (Championship) on a good day.
But maybe that's just because I started watching Argyle when we were in the old Division 2 and anywhere below that has felt like a dip from our natural position ever since. A colleague supports Oxford and always says they are massive just because they won a League Cup in the 80s.