I keep my Bitcoin air gapped as I think it's safer than on Trezor that requires regular firmware updates.. The Trezor wallet is only for smaller amounts as quicker to sign a transaction. Yes I will buy another Trezor should it fail, but I like knowing the seed words and pass phrase also work on an air gapped Electrum wallet.
So you think that Electrum wallet and operating system on your computer doesn't need any updates? 
I could argue that Electrum releases updates more often than Trezor is doing for their firmware.
You don't have to update Trezor device if you don't want to do it, except if there is some serious security issues with old firmware.
@OP My method for mitigating the risk of faulty or malicious updates is to only use reputable open source wallets. That alone should be enough, but for a little added security you can check the release notes of the updates and only install them if they have important security patches or added features that you would actually use. That way you can usually wait a long time before updating, by which time any exploits etc are likely to have been discovered by experts in bitcoin community auditing the code.
Another rule of thumb for me is to choose the most widely used of the quality wallets, since you'll have the largest number of people vetting the software. Also wallets that have been around for a long time and have an established track record of reliability. Electrum and Trezor are solid choices in both of those areas.