The lesson here is to avoid storing a large amount of funds on centralized platforms. If you must use them, then it should be just for very small transactions or those who are into trading on a daily business, but it shouldn't be used as a means to store your coins.
It's not that difficult to get a non custodial wallet, write out your seedphrase and store them in a secure place is it? So why would you want to risk the safety of your funds in the hands of centralized platforms? Let's try to play safe at all time. The cryptocurency space is filled with unseen circumstances that one would regret over and no one would enjoy going through such stress for their hard earned money.
Well, your suggestion to store a large amount of funds in a non-custodial wallet is excellent, and it's clearly safer if we have control over our wallet, which is clearly different from centralized platforms or custodial wallets, as you mentioned. However, we also need to realize that both carry their own risks. Custodial wallets carry the potential risk of losing our assets if an incident occurs, such as being hacked or even going bankrupt (or running away). Meanwhile, non-custodial wallets also carry the potential risk of asset loss, and this is usually due to the owner's own error or negligence, whether it's losing the key (seedphrase or private key), forgetting to back up, or even natural disasters, which are all possible occurrences.
So, in conclusion, we need to realize that storing our assets (especially crypto and on the large amount of) should be under our full control, and we must always take precautions to prevent negligence or mistakes.