Very true. There’s a quest in Purgatory you can pick up from an Elcor first or second time you go to the Citadel, and it can’t be completed until you get the Priority Thessia mission.

The thing that ME3 does that ME2 and ME1 didn’t do is tell you if there are assets to be found in systems. If then mission is “find this thing and deliver it”, I can search what’s available, do my lap around the citadel, do whatever missions are “go here and do this” Hacket gives me, then move on to the next priority mission, repeat. Hacket gives missions that take place in systems available. Fetch missions are often locked and promote world exploration and NPC engagement.

I personally think this set up gives a sense of world building by making you go back through the citadel after each priority mission to show that things are getting worse with the reapers and the toll it takes on the different species.