I keep my Bitcoin air gapped as I think it's safer than on Trezor that requires regular firmware updates..
Even if Trezor required no updates, the airgapped wallet would still be safer. Hardware wallets that require connection to an Internet connected computer are not airgapped.
So you think that Electrum wallet and operating system on your computer doesn't need any updates?
They do, but if they're installed in an airgapped computer as they say, then almost all the risks of not updating are mitigated, because the risk of not updating almost always has to do with an attacker compromising your device via some communication channel. If it's airgapped, you can't compromise it, unless physically.