Tor uses some kind of limited padding,
Tor Project Inc added netflow padding after someone started posting on netflow, general TA, and Sybil problems. Then TPI censored, banned, and booted them out after they kept publicly posting about TA and other insidious and inconvenient problems such as Sybil. Now with Sybil, like before with padding, they never credit mention the poster's work, and try to phrase claim that TPI was the natural origin self impetus source to do the pad and Sybil just at those moments in time, when they had decades to do that since they knew the weaknesses since decades... No, they were just getting exposed is why... lol. Just like their netflow padding doesn't do much, neither does their current Sybil proposal. Some interest in real security surely exists, but it definitely gets distracted by $ponsors who pay for other things, all to half of said money for decades has been from Government, which many define as a problematic source of conflictive influencing.
Afaik all backbone routers can be configured for packet or per-flow
At high line rates it takes serious HW to do full spyveillance capture or flows, sampled and aggregated flows are common for ISP service when those aren't needed.
can get packet logs whenever they want them.
They can "get" them, but there's no need to go external for that when they can just troll the output of their own private TOP-SECRET FVEY taps that feed into their global internet buffers at Bluffdale and elsewhere. Same for what they get from their Corp-is-aware feeds obtained under different "authorities".
Against the elephant? Tor's padding is totally useless.
Not only the elephants anymore. Netflow traditionally a quaint thing used by ISP's and LEA's to match up endpoints, subpoenas, abuse, bots, traffic stats, etc... it can work to some percent to follow some tor traffic cases, but it isn't a generalized form of TA. Today really anyone with a brain and some code can begin to general TA characterize streams of bytes counting and timing over various size windows, and hunt for that pattern where it also appeared on their other boxes. Good luck trying to make a factor of defense improvement against general TA without trying a fulltime enforced and reclocked base layer of dynamic chaff. Submit papers for acceptance into tor alternatives :) "Tor Stinks -- NSA"