Hi,
Thanks for your message and happy new year to you, also.
Sorry to hear about the trouble you’ve had. The important thing to try to discover is how the site was hacked. There are so many ways a website can be compromised. You’ll need to ensure you don’t have any files on your webhosting that shouldn’t be there – only WordPress files. Ensure file system permissions are appropriate, and that you don’t have any vulnerable plugins and themes installed and everything is up-to-date and at their latest versions.
If you have a vulnerability or backdoor on your site, then no, it’s unlikely Shield will prevent all types of attacks. A security plugin is only 1 component of good website security hygiene. You could switch to another security plugin, but if the vulnerability remains that allowed the first hack to happen, then you’re no better off.
I hope this helps you in some way to find the cause of the hack.