Being decentralized means being distributed or dispersed, your wallet is a piece of software, it doesn't mean because it can be used alone with its own configuration it is decentralized, just like my miner for which I can change the mining pool at any time or go solo mone is not decentralized either as it's one piece of equipment if it breaks this is it. Just like with bitcoin core, if your HDD crashes there goes your wallet, what you have might have left be a copy on a stick but you don't have redundancy in this case like bitcoin nodes do.