That saying, "Don't put all your eggs in one basket" seems to me to be true. Splitting your Bitcoin in multiple wallets has more advantages than storing it in one wallet, This is because scammers are constantly coming up with new ways to attack investors, so if you have all of your Bitcoin investments in one wallet and it gets compromised, you will definitely lose everything. Even if you're diligent about your security, there's the possibility that you'll fall into their victims and lose all of your life savings.
However, if you split your BTC into multiple wallets and one of them is hacked, there is no way that your entire BTC will be lost, and this strategy makes it easier to use one wallet as a long-term investment and the other one for your everyday spending, IMO.
Where I'll agree with you mostly is the case of seed phrases stored manually offline on a metal sheet or paper. It might be helpful to split funds in more than one wallet so that when the wallet is mistakenly or intentionally compromised, you'll only lose part of your holdings and the thief in question wouldn't think you've more since he already found one.
Again when you're held hostage or having a security breach based on your crypto involvement, you can surrender one of your wallets, gain your freedom and not having to lose all your coins in the process.