Ah yes, the question of interesting stuff. No matter how you slice it, "interesting" is a subjective opinion - but "rarity" is objective, you can measure it. Individual thresholds will vary, of course: for some, 1 in 50 systems counts as rare, for others, routine.
The FSS is faster if your concept of rarity is around body types, because it's faster to tell at a glance all the body types in a system. (The glaring exceptions are GGGs.) As the developers talked about it, body types are what they think makes a system interesting or not.
With the DSS's magical precision, and the FSS's magical (but currently deeply flawed) POI finder, as a secondary concern there is the presence of POIs on landable planets. But the developers know full well the quality of what is there to be found, hence why it would be secondary - to them.
For other kinds of rarities, if you're interested in things other than body types and POIs, you were negatively impacted by the FSS.
The problem, of course, is that these two targeted interests don't last long, and explorers over time tend to lose interest in them - and Frontier have made it much slower to find the more rare stuff. Not more difficult, just slower. Put another way: as player experience with exploration grows, "1 in 50" shifts from rare to routine.
So the solution to the stagnant activity would be either to add (many) more new things of interest, or to do whatever is needed restore previous functionality.
But the biggest problem against this is that Frontier have also demonstrated that they aren't much concerned about how the live game will fare before the next expansion. Since exploration has always been near (but not at) the bottom of the priority list, don't expect anything major to happen before the end of next year. (Assuming the expansion doesn't get delayed.)
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