As KiltedTim noted you can only derive Camera privacy benefits by upgrading macOS. Mojave or later I believe.
I use Skype for computer > landline phone calls only, no video or facetime calls.
You may be interested to know that Microsoft's acquisition of Skype incorporated Microsoft's ability to harvest personal information, including but not limited to the numbers you call, connection time and duration, files sent / received, chat history, etc. Microsoft uses that information in the usual manner—to sell you stuff. They are also free to share it with their business partners, vendors, etc, and all that information is subject to subpoena. As far as anyone knows Microsoft can retain that information forever.
Skype data are not encrypted, unlike FaceTime which uses end-to-end encryption (a HIPAA requirement should that matter to you). Ditto for iMessage.
Skype has also been target of malicious attacks that have successfully intercepted and recorded calls.
At least you can reassure yourself that if the FaceTime camera LED is "off", so is the camera.
I'm with KiltedTim. If you're concerned place a whimsical sticker over the camera lens. Leave the LED uncovered just in case.