That small cooling difference affects how these CPUs are clocked and how they behave under sustained workloads.
A long video render is easily 2-3h at 100% CPU load. A scientific simulation is >24h at 100% load, with instruction trains optimized to get every ooze of performance, hence hitting the TDP almost instantly.
A MacBook Air M1's body is not an unlimited heatsink attached to M1 SoC. I've succeeded to heat my M1 air to unusual levels when the platform was new and some programs were prone to entering infinite loops.