Bitcoin has 2 weaknesses.
1. The bitcoin encryption could be broken. Be it QC or a clever algorithm or whatever. That would make bitcoin almost worthless overnight.
2. The blockchain grows every day. Unless something is done, eventually it will become too big. And then one by one the nodes will quit supporting the network.
I'd like to address these constructively.
1. Technically true, without a doubt. But let's take note that Bitcoin's encryption being broken is going to be the least of our problems if the encryption was actually broken.
2. While Bitcoin's blockchain is indeed growing day by day(currently at 285MB according to Blockchain.com[1]), and that's with a decade of existing. It's growing really really slow, to the fact that technology is growing A LOT faster. A 1 terabyte micro SD card already exists for crying out loud.
Compared to gold, bitcoin is unsecure. Gold can't lose all of its value overnight.
Not sure how you even compare Bitcoin's security to a piece of metal to be honest. Also, remember that gold can a lot more easily be faked. To be completely sure if the gold you're receiving is actually legit, you'd have to do some chemistry or some applying of pressure or go ask some business to verify it for you.
[1]
https://www.blockchain.com/charts/blocks-size[2]
https://www.amazon.com/SanDisk-Extreme-microSDXC-Memory-Adapter/dp/B07P9W5HJV