The post that I replied to just said "
Have a look at the lvl 29 powers in 4E. Compare to synaptic static in 5E.".
And Synaptic Static is itself from a supplement rather than the PhB.
But in any event, here's a 29th level spell from the 4e PHB:
Hurl through Hell
Daily * Arcane, Fear, Fire, Implement, Teleportation
Standard Action, Ranged 10
Target: One creature
Attack: Constitution vs. Will
Hit: 7d10 + Constitution modifier fire damage, and the target disappears into the Nine Hells until the end of your next turn. The target returns to the same square it left, or the nearest unoccupied square, and is prone and stunned.
Sustain Minor: If you spend a minor action to sustain the power, the target’s return is delayed until the end of your next turn. You can sustain the power no more than three times.
Miss: Half damage, and the target does not disappear.
(It was later errata-ed, to "Hit: 4d10 + Constitution modifier fire damage, and the target disappears into the Nine Hells until the end of your next turn. The target returns to the same space it left, or the nearest unoccupied space, and is prone and stunned (save ends).)
As an attack spell, that's pretty different from Synaptic Static. (Even the errata-ed version.)
Here's the 25th level Maze spell:
Daily * Arcane, Enchantment, Implement, Psychic
Standard Action, Ranged 10
Target: One creature
Attack: Intelligence vs. Will
Hit: 3d12 + Intelligence modifier psychic damage.
Effect: The target is removed from play. At the end of each of its turns, the target makes an Intelligence check against your Will. On a success, the target returns to play in the space it last occupied or in the nearest unoccupied space of its choice, if that space is occupied. On each failure, the target gains a cumulative +5 bonus to the check.
(I've used the errata-ed version, because it's clearer in its rules terminology. In its play, it's the same as the original version.)
Its main difference from the 8th level 5e spell is the cumulative bonus to the check. But that is just one example of why 4e tends not to have the problem being discussed in this thread. (A 25th level wizard probably has a Will of around 40. A Pit Fiend, Monster Vault version, is level 26 with a +19 Int bonus. With the bonus it will get out, but doesn't have an even chance until its 3rd try.)
So anyway, I think these examples refute your claim about comparative power levels. And that's before I get to fighter abilities like, say, the 27th level Cruel Reaper, an encounter power (from the PHB) that lets the fighter make two close burst attacks, with a 10' shift in between them. That's stronger than a 20th level 5e fighter's 4 attacks.
Again, that's not my experience.
Here is Acid Wave:
Daily * Acid, Arcane, Implement
Standard Action, Close blast 5
Target: Each creature in blast
Attack: Intelligence vs. Reflex
Hit: 5d6 + Intelligence modifier acid damage, and ongoing 10 acid damage (save ends).
Miss: Half damage, and ongoing 5 acid damage (save ends).
The expected damage, at 19th level, is 17.5 (dice) + 6 or so (INT) + 10 (ongoing) = 33.5, or about 10d6. And it is a close attack, so it doesn't generate opportunity attacks. I don't think it's the best option for a 19th level wizard, but it's stronger than a 5e D&D 3rd level AoE.
Here is Cloudkill:
Daily * Arcane, Implement, Poison, Zone
Standard Action, Area burst 5 within 20 squares
Target: Each creature in burst
Hit: 1d10 + Intelligence modifier poison damage.
Effect: The burst creates a zone of poisonous vapors that lasts until the end of your next turn. A creature that enters the zone or starts its turn there takes 1d10 + Intelligence modifier poison damage. As a move action, you can move the zone 3 squares.
Sustain Minor: The zone persists.
Whether it hits or misses doesn't really matter - it is the auto damage that is meaningful, about 12 hp on each target in a square 55 feet on a side. This kills all minions in the area. And over (say) 3 rounds is a significant amount of damage on any target caught in the vapours - which can be moved. The main weakness is that it is poison damage.
I don't know what 3rd level spell in 5e you are comparing this to. Compared to 5e Cloudkill it has a bigger area, and does similar damage to what that spell does on a save (half of 5d8 = 11.25), and its movement can be controlled. And the existence of minions in 4e D&D increases the utility of auto-damage.
Here is Evard's Black Tentacles (the errata-ed version, which reduces the AoE from burst 4 to burst 3, but clarifies the way the effect works):
Daily * Arcane, Implement, Necrotic, Nethermancy, Zone
Standard Action Area burst 3 within 10 squares
Target: Each creature in the burst
Attack: Intelligence vs. Reflex
Hit: 2d10 + Intelligence modifier necrotic damage, and the target is immobilized (save ends).
Effect: The burst creates a zone of difficult terrain that lasts until the end of your next turn. Whenever a creature enters the zone, you can use an opportunity action to make the attack against that creature.
Sustain Minor: The zone persists until the end of your next turn, and each creature within the zone takes 10 necrotic damage.
The damage - an average of 17 or so - is modest, and necrotic is not a very good damage type. But immobilisation in that area is strong, and the creation of a zone of opportunity attacks that immobilise is really quite strong.
5e D&D has various area denial/restraint spells: Spike Growth, Evard's Black Tentacles, and even Slow can be considered through this lens. I'm not sure about their level rankings - Spike Growth is 2nd and Evard's 4th, but the former has a better range and AoE, and seems like it might be more useful in many circumstances. I think this is an area where 4e D&D just has a clearer sense of balance in the way it allocates effects to power levels.
Have you played high level 4e D&D? I have. The idea that a 19th level 4e character and an AD&D character of (say) 7th level are on a par - in the sense that they occupy the same sort of place in the fiction, and engage in the same sorts of adventures - is completely at odds with my experience.