I think everybody has a gimme on mentally filtering out "Obama" from "the dems" when speeches are involved, he's just so goddamn likeable when he's grinning and booming out words, pausing, and so forth.
I don't think HIllary would be less capable politically, arguably she's probably got a better chance at scoring points in the "nope, not gonna do shit" game against the house and senate republicans because she's been dealing with them, been dealing with being hated, and has a different enough style that she can hopefully push in a more productive way than Obama did against them. Kaine, while boring as hell, is a great option for working across the aisle there too, as I said before, nobody hates him, even on the republican side.
Still, I do a great Obama impersonation, and really enjoyed listening to him talk, I'm gonna miss that. He was funny and charming, Bill was sleazy but charming, she's not very funny or charming, but neither is der Drumpf, and she is less sleazy than him by virtue of not having to wear prosthetic skin to hide the truth that he is a gigantic gila monster.
As for WW3, nuclear powers don't just "start shit" like that. We'd have to find a russian sub dropping off spetsnaz in lake michigan while tanks rolled in across canada to invade minnesota or something before we'd just say "hey Russia, fuck you, we're squabblin' now", and similarly we'd need to like, annex the Ukraine and start siezing oil fields in Siberia before they'd be willing to jump up to "we need to start talking about where we nuke first" levels, and that's not even guaranteed.
Especially a politician who was involved in working to make sure WW3 didn't happen, Hillary may be hawkish, but she's not the unpredictable nujob candidate running this year.