Let's just say, PCMatic has caught more "bad internet pages" (preventing my access) than Norton/McAffe and from reviews and independent tests, PC Matic bested other non US commie based malware/ransomware software companies.
Maybe it is due to their unique method of using "white listing" (list of known safe files) for protection. Most virus apps use "black listing" (list of constantly evolving malware codes/algorithms) for protection. If it ain't on their list, you could get infected.
Most all malware/virus pros agree that Defender can be inconsistent and produce a higher rate of false positives. But more importantly, if you use Internet Explorer or Edge, then Defender's anti-phishing feature will work just fine. The trouble starts when you use non-Microsoft browsers like Chrome and Firefox (what I use). And what about smart devices, like my Android phone? Defender can't help you but PC Matic has you covered.
What computer/program optimization features are available on Defender? None. PC Matic has a nice suite of optimization tools incorporated.
BTW, isn't Defender Microsoft based? And with the now mandatory "Microsoft Account", Bill Gates and Company have full knowledge of Windows 10 users' actions.
If one thinks Microsoft Defender is more "private", that's OK with me; most of us know differently.
Added on edit: PC Matic only replaces Defender's virus/malware features--it is not an either/or.