The trouble with that is the same as calling first level something else like "level zero" or "survivor". The GM can no longer start this campaign with higher level PCs but these restrictions as a fair tradeoff when skipping the zero to hero levels fit the campaign. They can't do that because skipping them for seasoned to hero / hero to demigod or whatever is the default or level one. By contrast presenting the zero to hero campaign as punishing PCs with level zero/survivor/negative levels/etc automatically poisons the well by wrongly allowing a player to voice "I don't like that type of game" with obfuscated statements like "why do you want to nerf/punish/penalize/etc us, why should.." in a way that is impossible for the gm to even pretend that discussion was ever possible if the response is anything but a resounding and overwhelming cheer of support"I’d be fine with shifting the labels so that what is currently called “3rd level” becomes 1st level, and the current levels 1 and 2 become -1 and 0 respectively. In that case I’d still want a -2 with only race and background features and no class features. What number the levels have doesn’t really matter to me, though 5e does seem to prefer avoiding negative numbers.