Is there any advantage to running Windows Defender in real-time mode
if you're not using MS Internet Explorer? I prefer Firefox. I have no
other network connections.
Microsoft is not in the malicious software detection/removal business.
You should find a company(s) that is in the anti malicious software
business and use the products that suit the needs of your environment
and Internet habits.
WD is also slow to come out with definitions of new threats. Once a
month, once every two weeks - depends on where you get your questions
answered.
There are some very good third party products that update sometimes
daily, or more than daily and have very good detection/removal
ratings.
Several with real time protection are known to be heavy system
resource consumers and don't play well with other applications.
No single program is likely to know about every threat, so you should
have more than one.
Many respectable ones are free, but may not offer any real time
protection for free - they are manual updates/scans, but that is fine
for a lot of people.
The more features you want/need may want you to have a paid
subscription to get those features.