there isn’t a single hero in the game that doesn’t bring something ‘replaceable’ by another hero. That is to say, what any hero does, another hero can do as well.
If you’re pressed on it, then you’ll probably just move the goal post more and more cuz the point isn’t the particulars of what is ‘replaceable’ but rather, that you think she is the worst.
Part of the issue for Nova is that the sort of tasks she could fill have been power-creeped elsewhere. Scouting tools don’t do much because other heroes don’t have enough mana tension to be punished for scouting bushes and corners with their own abilities, so utility for ‘scouting’ effects is lost.
Similarly, sudden damage bursts from “out of nowhere” are “anti fun” so the metrics of how she deals damage has to be staggered and delayed such that other heroes tend to get their stride earlier.
If she had other utility then it offsets the point of an invis hero (to be invis) but even then, of the effects that nova has, she does get debuffs earlier than other ranged heroes, so as a utility deeps, she actually is a bit better that other picks – which tend to come from healers instead – so part of the issue of the game picks is that players expect nova to be lead dps, and in that area, yea, other heroes have better opportunity to deal damage from further away, with lower mana costs, and more waveclear.
But as a damage-enabler? Yea, there aren’t very many options that suit that role (tyrande being the most notable) but at the end of the game, boosting the stats of other heroes doesn’t reflect well on the utility hero, so it’s no small wonder people overlook that in favor of padded stats they can admire instead.
Does something need to change for nova to make her ‘better’? Arguably yes; she could have a better fit for utility options, reference more ghost stuff, or get a ‘tassadar’-like rework to shift some of her ability set in a way to make room for other heroes (eg spectre pants mcvoodoo) or to have a unique tool-rotation kit that references the Nova spec-ops expansion.
Part of the issue for Nova is that she’s a poster-child that didn’t have her poster-product actually see the light of day, so what ‘fantasy’ that would be particular to her is spread out over a bunch of partial iterations. The same thing happens for Valeera where she doesn’t have a personal fantasy to represent, and is a generic reference to a span larger than she should have.
That especially doesn’t help that both are ‘stealth’ heroes, so they have this section of their power pie that doesn’t suit as well their role as slotting another hero that just doesn’t have stealth, or rather, could just be granted stealth from another hero instead.