No, I agree. It looks like a slightly less severe version of 3e's save disparities. But still, yes, it appears they didn't learn from previous editions' mistakes.
A 20th level Wizard will have a save DC of 19. Even with Advantage, that's a hard target to hit with a +0 (or god forbid - 1) stat modifier. So Hold Person, even if it allows saves every round, will be an encounter ender vs. Fighters and other beefy targets.
... you know, I don't see an issue there.
Hold Person in 5e is concentration-based, which means your 20th-level Wizard can only Hold one Person at a time. There will be disruption mechanics for that, so the rest of the party can attempt to free them. They can't cast it on the entire party and, if they could, that would mean you had an entire party's worth of 20th-level Wizards.
If you're fighting a group of - or even one - Wizard with 20 PC levels, you're facing a serious challenge and you should be seriously strong. For a start, it's not at all unreasonable to think that if you're facing a 20th level challenge, even your *secondary* stats might be close to 20. Even without proficiency, you could have a +5 saving throw. That would give you a one in four chance of breaking the spell every round.
This all looks entirely reasonable to me. We're talking about an epic battle, probably the climax of an entire campaign. There *should* be amazing powers flying about the place. Hell, let's look at this the other way around - imagine a Wizard facing a 20th level Fighter. Given the Wizard in the Hold Person example got to cast first, let's make the fighter win initiative.
So, the Wizard probably has a low armour class and the Fighter probably has picked up one of the weapon specialisation feats - let's make the Fighter an Archery specialist, to make up for Hold Person being ranged...
The Wizard might have an AC of 18 (mage armour with +5 DEX). The Fighter has +13 to hit (+6 proficiency, +5 DEX, +2 Archery fighting style).
The fighter uses an Action Surge to take two attack actions for a total of 8 attacks. With +13 to hit and getting a critical hit on rolls of 18, 19 or 20, that would do an average of 70.4 damage in a single turn and (statistically speaking) at least one "Devastating Critical" - which means until it gets treatment, healing or dies it's taking 1d6+10 damage at the end of every turn.
A 20th level Wizard with a CON of 10 would have, on average, 82 hit points - which means it would be guaranteed to die after taking its first action, unless it's able to get treatment or healing (which would almost certainly cost it an action). If the Wizard has a CON of 20, it would still have lost nearly half of its 182 hit points in a single round (over half if you include the devastating critical effect). The fighter can take another action surge next round... things are not looking good for the poor 20th level Wizard.