Are Layer 2s as secure as Layer 1?

So fees on the mainnet continue to be a problem. I'm sick of paying $5-6 for fees. Today I got a warning about congestion and that fee estimates couldn't be relied upon.

I was thinking of moving all my coins over to Arbitrum or Optimisim which I've used successfully many times before. Arbitrum is widely supported by exchanges in my experience, a bit more than Optimism.

But are Layer 2s as secure? Can they be depended upon yet to keep your coins safe?