I'd be for buffing the weakest of the weak to make them slightly more viable. There are Pokemon who aren't even decent in NU that could use some form of help. Pokemon like ... Spinda, Delcatty, Farfetch'd, Delibird, Luvdisc, Mawile, Volbeat/Illumise, and every electric rodent ever.
For other Pokemon who need just an extra push to be great another ability or an expanded movepool. Some Pokemon just need reliable recovery. Others need offensive moves to go with their offensive stats. They're getting better at fixing what's wrong with certain Pokemon.
Or Ledian who got Iron Fist and lost the Elemental Punches + Mach Punch.
I think that certain abilities helped Pokemon that were decent before find the niche they needed to become great. Espeon, Ninetales, Politoed, Venusaur, Alakazam, and company are clear winners. Then there's the bunch that got their old abilities buffed like Gastrodon and the Sturdy Pokemon.
Then there are Pokemon who was terrible and will be terrible regardless of what they do to try to balance the game. A good example is every Pokemon that got Contrary. It could be a great ability on some Pokemon, but the three Pokemon who got it don't have the right tools to truly abuse the ability. Shuckle has no offensive power, Seperior has few offensive moves, and Spinda has
nothing.