This is nonsense. The password storage function of browsers is very useful. I wouldn't recommend it for your most sensitive passwords like ebanking, credit cards, or the like, but for website logins they're perfect.
"If your device is ever stolen and a thief guesses the access password"
If your device gets stolen you have other problems to worry than a Fandom account. Also, this isn't much different as if they guess any other password, especially since many people use the same passwords for several or all their logins. It's also not different than when they guess your email password where they can most likely even find ways to restore and change your logins for many services.
And in case of
"or steals that too"
you're lost anyway.
It's much easier to create and remember one (1) strong password than to have dozens of different passwords for all your low/medium level online accounts that you need to store or write down somewhere to remember. Again, I'm talking of low to medium level online accounts. Fandom isn't your banking account.
"Additionally if you leave a device on"
This again isn't any different whether you store your logins or not.
As you can read here and elsewhere every few days, people tend to never log out of services, for reasons I will never understand as this is terrible in regard of privacy and security, but it shows the widely spread lack of awareness of online security.
If devices, especially mobile devices like phones, tablets, and laptops, are left unlocked so they can be accessed by not matter if it's relatives or a thief, then again you have much bigger problems than a compromised Fandom account. Security begins a few levels higher up, by NOT leaving devices unlocked when you don't have control over them, and lock themselves when they're not used for some time.
Considering how most people use online services, logins, and their devices, and how they value or are aware of online security, which unfortunately is best described as "lazy" at best, and "non-existant" way too often, using a password manager (or the browser's equivalent function) is the much better option than most alternatives most people practise (if at all).
Remember, we're talking about practices like, [quote:] "I never sign out, even when I'm not using/posting on Fandom. (I avoid signing out so that I don't have to always put in my password every time)"
Overall, this is a very broad topic that cannot be handled in a discussion post or three, but believe me, I'm a very much security and privacy concerned person, and I deal with that topic for several decades already, not only for myself but also for friends, relatives, and customers. For most common people who are not security nerds, using password managers is the much better option than what they do otherwise.
