why is zard still ranked lol
Because it isn't really completely outclassed by anything. 100 base speed is pretty good and in Sun with Specs it 1-2HKOs literally everything not immune to fire. Darmanitan is better in a lot of ways but still has issues with recoil and is a little slower. It also has worse defensive typing giving it fewer switch-in opportunities. Charizard also has Hurricane which can OHKO unsuspecting Pelipper on turn 1 making it somewhat decent even if the weather gets rainy. Similarly Weather Ball works in Rain, Hail, and Sand against different targets. It's a lot more versatile than Darmanitan.
252 SpA Choice Specs Solar Power Charizard Weather Ball (100 BP Fire) vs. 252 HP / 4 SpD Blissey in Sun: 375-442 (52.5 - 61.9%)
252 SpA Choice Specs Solar Power Charizard Overheat vs. 252 HP / 4 SpD Blissey in Sun: 486-573 (68 - 80.2%)
252 SpA Choice Specs Solar Power Charizard Weather Ball (100 BP Fire) vs. 252 HP / 4 SpD Toxapex in Sun: 179-211 (58.8 - 69.4%)
252 SpA Choice Specs Solar Power Charizard Overheat vs. 252 HP / 4 SpD Toxapex in Sun: 233-274 (76.6 - 90.1%) -- 25% chance to OHKO after Stealth Rock
252 SpA Choice Specs Solar Power Charizard Overheat vs. 0 HP / 4 SpD Multiscale Dragonite in Sun: 157-185 (48.6 - 57.2%) -- 94.1% chance to 2HKO
Even Heatran has to be careful.
252 SpA Choice Specs Solar Power Charizard Focus Blast vs. 252 HP / 136+ SpD Heatran in Sun: 396-466 (102.5 - 120.7%)
252 SpA Choice Specs Solar Power Charizard Scorching Sands vs. 252 HP / 136+ SpD Heatran in Sun: 464-548 (120.2 - 141.9%)
These calcs are Timid, if you have giant balls run Modest to OHKO Toxapex with Overheat. The damage output from Charizard is ludicrous. Also for comparison purposes with Darmanitan:
252 SpA Choice Specs Solar Power Charizard Weather Ball (100 BP Fire) vs. 0 HP / 0 SpD Mew in Sun: 486-573 (142.5 - 168%)
252 SpA Choice Specs Solar Power Charizard Overheat vs. 0 HP / 0 SpD Mew in Sun: 631-744 (185 - 218.1%)
252 Atk Life Orb Sheer Force Darmanitan Flare Blitz vs. 0 HP / 0 Def Mew in Sun: 526-620 (154.2 - 181.8%)
252 Atk Choice Band Sheer Force Darmanitan Flare Blitz vs. 0 HP / 0 Def Mew in Sun: 604-712 (177.1 - 208.7%)
Is it something you can slap on any team? Absolutely not. But it's a Sun team Fire type nuclear bomb so I'd argue it fits next to Darmanitan in C-. Far from the best in the tier but it does have a niche.