Did you recently upgrade to Pega 7.2 from an older version of Pega? Starting in Pega 7.1.8, we re-architected the concept of rule delegation. As part of this new architecture, rule delegation has been de-coupled from "Favoriting" a rule. Adding something as a "Favorite", which you correctly describe, was the previous mechanism for rule delegation in the past. A developer could "favorite" a rule, assign it to an access group, and then members of that group could interact with the rule from the case manager portal via the "My Rules" menu option. The version of pyCaseManager Navigation rule which ships with 7.2 no longer has the "My Rules" link in it, but you can certainly add that into your menu if you wish. The click action just launched the pyCMDelegatedRules harness, which is still in the platform.
Why did we redesign the delegation feature? There are several reasons. Even though the old 'Favorites' model of 'delegation' supported any rule type, it came with a host of problems that caused confusion to many users. Opening a 'delegated favorite' using "My Rules" opened the rule in it's entirety, and customers rightfully complained that their business users had the ability to change anything they wished - including things like rule availability, ruleset, ruleset version, etc. The new delegation model solves these issues by presenting a business-friendly facade in front of each delegated item. (Try delegating a new decision table and you will see what I mean).
The new delegation model supports data types, decision tables, paragraphs, map values, and correspondence records. We add support for additional rule types in each release, based on customer feedback. You can use the Actions > Delegate action from the rule header to delegate the item to a particular access group. The System-User-MyRules class is still used to store these delegations, but they are tracked via "DelegateAG", as you've already discovered.
Now, to address your specific question about Data Type delegation. It looks like you've already delegated this using Actions > Delegate from the data type screen. Members of your target access group will find the delegated data type, (as well as all other delegated items), listed under the Configuration navigation item in the Case Manager portal. Users whose access group do not have any delegations assigned to them will not see the Configuration nav item.
So, to summarize:
1. Several ruletypes, as well as data types are now delegated to a target access is group via Actions > Delegate in the Designer Studio.
2. The concept of "Favorites" is still in the system, and you can use it for bookmarking rules. "Favorited" rules appear in in Favorite Explorer in Designer Studio
3. Rule instances previously marked as a favorite as a means of "delegation" should be re-delegated using the new Actions > Delegate construct, if possible
4. "My Rules" is no longer displayed in the Case Manager menu, although you can add it back in if you wish to continue using old 'favorites'
5. Delegated rules, including data types, can be accessed under the new "Configuration" nav item in the Case Manager portal.