-DK
-Kirby
-Luigi
-Jigglypuff
-Bowser
-Marth / Lucina
-Mr. G&W
-Ike
-Mii Brawler
-Shulk
-Bayonetta
-King K Rool
-Incineroar
So let's logically look at this list and what they can do against Hero, should they be full stage at any given time.
-Kirby has the air. What can Hero do against Kirby in the air? Hope for Magic Burst and then leave himself mana starved? Hope to bait a kamakazi? I'd be willing to bet Kirby is in the stock lead among equally skilled players. Not a good option. Pray for a Thwak and hope Kirby just floats in front of him for it to hit? Kirby can just float all around and ignore just about every spell Hero has. He'd be better off selecting a buff and hoping to land a solid hit. When Kirby gets in (and he will) Hero will get combo'd and put back in disadvantage (And honestly, disadvantage for Hero is anyone being closer than half stage). You could also force a menu drop with Up Special, using the projectile portion to cause Hero to react, unless he has an answer in his Menu which you've had ample time to observe while floating around.
-Jigglypuff again has the air. Same game plan with Kirby. Float around and make Hero sweat. You don't even need to do anything aggressive. Just being close is enough to make Hero drop the menu. Playing this game of 'chicken' with his very few AOE spells is not likely to happen unless he is Menu shuffling while you float around. You pressure just by existing in an uncomfortable closeness, ala Kirby.
-Bowser is fast. Bowser should have no trouble closing the gap. Even being big shouldn't matter much. You can react and shield many if his projectiles, or hop over and before he can recover, Bowser is now chewing on his face...or at the very least...making him uncomfortable with how close you suddenly are. What is Hero going to do about that now? Open the Menu in striking distance?
-Marth/Lucina? Should I have to make an argument as to how, arguably, the best swordies in the game harass a projectile user and keep up constant pressure with their amazing movement speed and air speed? One whiffed spell is all these two need to get in and put on stock threatening damage to Hero. They literally bait and chase, it's been their plan for a while and one they don't suck at.
-G&W Bucket. Literally answers every projectile move, not to mention he can duck most spells due to how small he is, or just Up B and glide into position. He only fears Kamakazi and Magic Burst which again are situational or put Hero in bad situations if they whiff.
-Ike I'd agree suffers a little more than most but every Ike I've played has zero issues keeping on me and even Ike has better frame data than Hero and is actually faster. His air speed is decent to hop over spells thrown (Or block) or counter if he feels ballsy.
-Brawler's options entirely depend on his load out. I'd imagine the psudo-ZSS flip kick is going to work wonders on not only covering the gap but getting a punish on the second attack. Yet even with out it, I'm just going to repeat myself. JUMP OR BLOCK.
-Shulk has monado to give him either speed or jump. There is no way he isn't getting across the stage to deal with a Hero sitting there with his menu open. And if the Hero isn't rapidly cycling his Menu and just sitting on one screen, you know what he has. You can bait it, you can punish it. Or just go Defense as you get closer and you're not going anywhere no matter what you might get hit with (Unless Thwak or Whack but...why are you getting hit by this).
-Bayo has great air options to traverse the entire stage without landing once. She can also shoot him with her neutral special to force him out of the menu. She can also Witch Time a spell thrown her way if feeling ballsy...or just block then resume her approach.
-K Rool might have the hardest time of the lot if he's finding himself on the other side of the stage. Depending on stage, he has platforms though. Hop along those. Ballsy = belly reflect any spell thrown or the safe option is...block. he's faster than Hero so gaining distance even on ground isn't too much a challenge. He's still big so I confess, a bad character in general is going to have a hard time no matter the match up.
-Incineroar is one slow boy but he is often underestimated. Revenge damaging projectiles if you feel bold or use your air options to traverse. You've got double jump, you can stall a bit with Fspecial and when in position, you can even try to use Cross Chop to hit Hero while he's sitting there (Even go through plats, or mix up by not going through the plat like they may expect and you've not only forced them to drop menu but now in their space). From there you play some cat and mouse as Incineroar does with most everyone but Hero isn't so fast as to outrun you and STILL get that menu back open.
While I may sound repetitive...block and jump solve 95% of the options Hero has when his Menu is open. None of them are unblockable sans Kamakazi.
As for full stage length away? With what Spell? His fireball goes fairly far but not full stage, is slow and reactable. Sizz and Kaboom? Sizz is shorter ranged and Kaboom is likely the one to do the job with the vacuum effect before explosion but can be blocked before the explosion happens. Thwak and Whack aren't getting you from full stage. Nor is Kamakazi or Magic Burst. His side special isn't hitting you full stage. Sleep isn't full reach and isn't going to kill unless it manages to hit and Hero runs all the way across the stage before you mash out of sleep. The rest of his spells are buffs, heals or slashes.
So...how is anyone 'reasonably' getting killed full stage by Hero?