Charizard is definitely overrated, being the OG Dragon we all got to own as a kid/teen/young adult/adult/etc. However it is not completely without Merit. While Fire Flying is plagued by common weaknesses in Water, Electric and a cripping 4 times weakness to Stealth Rock, 6 resistances and 1 immunity plus dodging every other entry hazard isn't bad... Though, Stealth Rock, Solar Power, and Charizard's own poor defenses ensures it has little defensive utility.
What Charizard brings to the table is Power... in the sun. Solar Power + Specs, or heck, even Life Orb has obscene power with the number of Pokémon commonly used in Doubles, OU and Ubers that are not threatened by a OHKO by Solar Power Specs can be counted on two hands (using Overheat/Solar Beam and Focus Blast for coverage). Base 100 Speed is appreciably fast as well. While 8 generations of Power Creep have ensured that Base 100 isn't impressive against a number of offensive Pokémon, against defensive ones, base 100 speed is lightning quick to them, turning Charizard into a fierce Wallbreaker melting anything not named Blissey/Chansey, Armarouge, Ceruledge, intact Multiscale Dragonite, Rotom-Heat, Specially Defensive Skeledirge, Ting-Lu, Toxapex or Miraidon.
However, Stealth Rocks being extremely common in Singles ensures that Charizard will likely continue its reign of lording over the lower tiers, but in Doubles, I can see Charizard having a niche like in previous generations. Sun has never been stronger, especially with the Scarlet Paradox Pokémon running about, making it relatively easy to slot Charizard on a team with Sun Support and Start melting the competition. However, losing Dynamax hurts and Charizard no longer has an emergency button to compensate for its bulk, a STAB Attack that increases its speed, ignore the drawbacks of its stronger Fire Attacks or still have a Grass attack available when Sun goes down. Sadly, Charizard isn't currently allowed in VGC, but I expect that to change in the future.
Ability: Solar Power
Item Attached: Life Orb
-Focus Blast/Ancient Power
-Solar Beam/Flamethrower/Fire Blast
EVs and Nature:
4 HP / 252 SAtk / 252 Spe
Timid (+Spe, -Atk)
Charizard in Doubles proves to be an intense threat in the Sun. Only Armarouge and Ceruledge are directly immune to Charizard's Fire Attacks which do obscene damage after sun comes up. Heat Wave provides good spread damage at little drawback, making it easy for Charizard to pick up KOs on weakened teams. Focus Blast provides invaluable coverage into Roaring Moon and Tera Normal Dragonite, while Ancient Power provides coverage for many opposing Fire types (Arcanine, Torkoal, Armarouge, Iron Moth, Tera Fire Hydreigon ,etc.) Solarbeam has naturally fantastic coverage with Fire, but if you already have several Grass coverage on your team, swapping out for a non-Spread Fire Attack is worth consideration. Protect is the best move in Doubles.
Tera Fire is preferred -Charizard's power when Terastalized becomes obscene, reaching numbers it would otherwise have to use Overheat or Blast Burn for without the drawback. Tera Grass is a viable option, giving STAB to Solar Beam while wiping out many of Charizard's weaknesses.
Torkoal is king. You need that sun up, Torkoal provides.
Tailwind setters are also invaluable, patching up Charizard's speed to get the jump on the faster offensive threats like Flutter Mane and Iron Bundle.