Yes, AdX is better than AdSense. Google AdX, when optimized correctly, gives a 30-50% rise in ad revenue in tier-1 Geos (Australia, Austria, Belgium, Canada, Denmark, Finland, France, Germany, Ireland, Italy, Luxembourg, Netherlands, New Zealand, Norway, Spain, Sweden, Switzerland, United Kingdom, United States of America).
ADX has better demand and ECPM (more networks and agencies)
Whereas AdSense works better in tier-3 Geos and does not have a minimum traffic requirement like in AdX where the minimum traffic requirement is 5 million visitors per month.
(Adsense can be accessed separately via GAM as well)
AdSense is an independent platform with a dedicated dashboard, whereas AdX is accessed by Google Ad Manager and needs MCM partners (like AdSparc), (not needed for GADX operation experts, and tech developers) to run. Clearly, AdX is suited for big publishers in tier-1 Geos, and AdSense works better for smaller publishers around the world. Based on user case.