Your comparison doesn't show what you think it does. All it does is show the power of a pretty presentation.
It doesn't look that much simpler to me. There are a lot fewer skills and no feats, but otherwise the only difference is the 5E version has fewer tactical options.
Yeah, that was a bit of a formatting trick. Even WotC realized the 3.X statblock was a wall of garbage and changed it low-about DMG2 era (which the Pathfinder, 4e, and 5e statblocks now emulate).
In the interest of fairness, here he is in the later statblock.
[sblock][TABLE="width: 100%"][TR][TD]
Red Dragon, Adult
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CR 15
[/TD][/TR][TR][TD="colspan: 2"]Always CE Huge Dragon (Fire)
Init +4;
Senses blindsense 60 ft., darkvision 120 ft., keen senses; Listen +31, Spot +31
Aura frightful presence (DC 24)
Languages Draconic
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AC 29, touch 8, flat-footed 29
(−2 size, +21 natural)
hp 253 (22 HD);
DR 5/magic
Immune fire, sleep, paralysis
SR 21
Fort +18,
Ref +13,
Will +17
Weakness vulnerability to cold
[/TD][/TR][TR][TD="colspan: 2"]
Speed 40 ft., fly 150 ft. (poor)
Melee Bite +32 (2d8+11) and 2 Claws +30 (2d6+5) and 2 Wings +29 (1d8+5) and Tail Slap +29 (2d6+16)
Space 15 ft.;
Reach 10 ft. (15 ft. with bite)
Base Atk +22;
Grp +41
Special Actions breath weapon (50 ft. cone of fire 12d10, DC 26), crush 2d8+16 (DC 26)
Spell-like Abilities (CL 7):
6/day—
locate object
The save DCs are Charisma-based
Typical Sorcerer Spells Known (CL 7):
0— (6/day)
arcane mark, dancing lights, detect magic, ghost sound, mage hand, read magic, resistance;
1st— (7/day)
alarm, divine favor, magic missile, protection from good, shield;
2nd—(7/day)
cat’s grace, darkness, shatter;
3rd— (5/day)
dispel magic, protection from energy.
[/TD][/TR][TR][TD="colspan: 2"]
Abilities Str 33, Dex 10, Con 21, Int 16, Wis 19, Cha 16
Feats Alertness, Empower Spell, Flyby Attack, Multiattack, Improved Initiative, Power Attack, Weapon Focus (bite), Weapon Focus (claw)
Skills Appraise +16, Bluff +16, Concentration +18, Diplomacy +16, Escape Artist +13, Intimidate +16, Jump +24, Knowledge (any 2) +28, Listen +31, Search +28, Sense Motive +17, Spot +31, Use Magic Device +16
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Blindsense (Ex) Dragons can pinpoint creatures within a distance of 60 feet. Opponents the dragon can't actually see still have total concealment against the dragon.
Breath Weapon (Su) A red dragon has one type of breath weapon, a cone of fire.
Crush (Ex) This special attack allows a flying or jumping dragon of at least Huge size to land on opponents as a standard action, using its whole body to crush them. Crush attacks are effective only against opponents three or more size categories smaller than the dragon (though it can attempt normal overrun or grapple attacks against larger opponents).
A crush attack affects as many creatures as can fit under the dragon's body. Creatures in the affected area must succeed on a Reflex save (DC equal to that of the dragon's breath weapon) or be pinned, automatically taking bludgeoning damage during the next round unless the dragon moves off them. If the dragon chooses to maintain the pin, treat it as a normal grapple attack. Pinned opponents take damage from the crush each round if they don't escape.
Frightful Presence (Ex) A young adult or older dragon can unsettle foes with its mere presence. The ability takes effect automatically whenever the dragon attacks, charges, or flies overhead. Creatures within a radius of 30 feet x the dragon's age category are subject to the effect if they have fewer HD than the dragon. A potentially affected creature that succeeds on a Will save (DC 10 + 1/2 dragon's HD + dragon's Cha modifier) remains immune to that dragon's frightful presence for 24 hours. On a failure, creatures with 4 or less HD become panicked for 4d6 rounds and those with 5 or more HD become shaken for 4d6 rounds. Dragons ignore the frightful presence of other dragons.
Keen Senses (Ex) A dragon sees four times as well as a human in shadowy illumination and twice as well in normal light. It also has darkvision out to 120 feet.[/sblock][/TD][/TR][/TABLE]
However, I disagree with the notion it really has "fewer" options by commenting how many of the options the 3.x dragon had were all that useful. Locate object as an SLA? The Crush attack? Power Attack? Do any of those options REALLY change the fact the dragon is going to primarily use its breath weapon and then do the dragon-dance attack (claw claw bite, wing, wing, tail)? to maximize damage?
The only tactical limit I see is spells, which can be restored either in the MM variant or by slapping spellcasting on via the DMG. (And IMHO, it emulates the Basic/1e Dragons where they had a % chance to cast spells.) And honestly, it can use up 5 spells up to 4th level all once per day: Magic Missile, Shield, Protection from Energy, Dispel Magic, and Stoneskin. Done.
Beyond that, the dragon got rid of its artificial DR/SR and replaced its sleep/paralysis immunity with legendary saves. To be honest, accounting for spellcasting variants, both dragons will probably run the same way in most combats.