I assume you have never experienced extreme performance summer tires then? They stick like F***ing glue in a turn compared to max performance summer tires. Although the sorter diameter is definitely only going to help. I assure you, Extreme performance summer tires are worth seconds regardless of diameter change. If they were autocrossing, the time reduction would have been much greater.
Actually I ran low profile Hoosiers when I won my class in SCCA SOLO II so yes I actually do know what real "stickies" are and I can tell you they were far more sticky than anything they have in this video.
The real performance difference is in the diameter and over all weight change per tire/wheel combo for acceleration, deceleration and handling with the shorter sidewall, as it was said they were running stock, summer, then max performance summer on each car. But they did change rims and from the looks of it aspect ratio of the one set the BRZ had which ruins a true tire comparison.
Oxford White 2015 Premium GT with 50-Year Pkg | 3.55 Gears | Roush CAI (105mm Velocity tube) | Stainless Works Headers (Jet-Hot ceramic coated), high flow cats, H-Pipe CatBack full 3" with 4" tips| BAMA V2 93 Octane Tune | Baer EradiSpeed-Plus 2-Piece Rotors | JLT 3.0 Oil Separators | FRPP M-20201-M STB | Silver PP Wheels 19x9, 19x9.5 | NITTO G2 255-40-19, 275-40-19 Tires | J&M Jacking Rails & Subframe Alignment Kit | Steeda Subframe Connectors & Bushing Supports | BMR Front Subframe Brace | Cervinis 1232 Functional Ram Air hood | Ford Performance door sills | White Madness Garage Chrome Shifter | Diode Dynamics interior LED conversion stage 1 & XP80 reverse light | 3M Dark Ceramic Tint (25% sides/20% rear) | Lloyds "50 Years" floor and trunk mats...
Performance White 2012 Premium Pony Package | Torsen T2R 4:1 TBR | FRPP 3.73 Gears | GT500 Differential Cover | DSS 3.8" Carbon Fiber DS | Airaid CAI | BAMA 93R tune | Baer DecelaRotors (drilled/slotted) | BMR Adjustable Panhard & Brace | JLT Oil Separator | Boss 302 STB | Nexen N3000 255-45-ZR18Y tires | PP Engine Cover | 25% Tint All cars should be rated for Smiles Per Gallon!