Depends on your first line and compensating controls. Would using Defender at the desktop be sufficient stopping enough malware on its own? Do you see your other controls detecting malware before hitting your desktop? What do your other network level controls look like? For example, BADs, Nbads, 802.1x, sandboxing at the firewall, ingress screening and many others all have their place at the table.
I am currently consulting for a major US based retailer that uses Defender and from a security standpoint, works quite well next to all the other goodies capable of supporting a well managed security platform.
If you can cut some money out of your budget and gain more security elsewhere, go for it. Keep metrics on your before and after statistics concerning number of detections, infections, events, incidents and breaches (pro and con) to prove or disprove your A/V choice down the road, of course. Like any business purchase the "proof is in the pudding". Always be prepared with metrics to defend your purchase or revert to more expensive solutions.
Personally, having not seen my home machines detect anything since the mid 1990s, stopped subscribing to expensive malware suites about a year ago and simply use Defender on all my machines. Backed up by a small firewall with an open source NIDS, daily backups, etc. Its all "delightfully excessive" (overkill) of course but that's a trade off for being a security person, isn't it?
