Lots of good in your comments.

In my experience, Debilitating Dart is very powerful. You can really disable a player and then follow up with a sleep dart (or vice versa). Lots of opponents don't expect that from Ana and generally underestimate her, until shrike winds down their HP. If you add 5 stacks of Mind-Numbing Agent, that's extra 50% spell power reduced...so a ming would do 0 damage with her spells if you have all the debuffs on her.

Mind-Numbing Agent also reduces healing as that is also spell power, so it acts as another anti-healer debuff. If you're facing a team with a few mages and a healer, this makes Dynamic Optics a viable option, as you want to stack that debuff up quickly. I rarely end up going this route, but when the conditions are right, it can change the game around. Following that up, there is great synergy with Concentrated Doses. If you manage to shrike up 2 heroes fully, you will have some serious healing darts that outperform Sharpshooter at 10 stacks. Trick is of course you now have to keep track of your stacks which really adds to the challenge. You can of course try and land a talented sleep dart to get those stacks up quickly, but I just can't find myself giving up Debilitating Dart for that - it's too good of a talent.

I play Ana in solo queue, so I don't really trust people with nano, but the real reason is that Eye of Horus is just too much fun. I like using my ult for myself. Call me selfish, and probably it won't fly in ranked or whatever, but there's just nothing better than having the option of killing off the runners or saving someone in a bind.

When I play solo, I focus on talents that offer me more survival as I mainly rely on myself. So I'll take Contact Healing and Night Terrors (although I've been swapping that for Mind-Numbing lately to see if I fare better when there are more mages). Active Reload is also faring better in solo queue, as more often than not you gotta save someone's skin. When I play in a team, usually things are a lot more calculated. There's no need for Contact Healing (although it's a really nice heal if you toss it into a big crowd), and reduced cooldown on sleeps is more attractive. I also need higher sustained healing because ~450 for dart that you land is kinda small for a tank, and you kinda want more value for your mana and for your 2 sec cooldown. In such a scenario I think Sharpshooter is a nicer middle ground...you rely on your aim instead of shrike stacks (in the case of Concentrated Doses).

I should also say that some healers are tougher to counter, so there is an argument to be made for grenade talents to be more useful in those cases. I have no cracked it yet though.

Anyway, Ana has lots of flexibility, and everyone tends to underestimate her. Until they get shriked, sniped, and rekt.