Are polar bears the largest land predators?

Polar bears are the largest extant predator that is adapted for land. That's indisputable. But labelling them as 'land predators' strikes me as an odd choice.

Marine-based Animals as Food

To be land predators, polar bears would have to hunt on land.
     Polar bears are creatures of water.
Polar bears hunt on sea ice. Ice, being water, cannot be classified as 'land'. 
     Ice is where they spend most of their time. Why they developed their camoflage. Why they can swim for days on end. Everything that makes a polar bear a polar bear is directly related to cold seas.
     All the species that polar bears rely upon for food (such as seals, walrus and whales) are marine creatures. Marine, as in not terrestrial, as in not land.

Yes, polar bears do scavenge washed-up animals on the shore. 
     But these are its usual marine prey of seals, walrus and whales. They might be eaten on land, but they were delivered unto land via the sea. 
     Plus, as this is scavanging, not predation, this behaviour can't be used to show polar bears are land predators.

Terrestrial-based Animals as Food

Yes, polar bears can eat land-based food. 
     If polar bears are on shore for long enough, fasting becomes difficult, so they will look for food on land. But this food lacks the high-energy blubber necessary to keep polar bear bodies working. 
     Also, polar bears typically scavenge food whilst on land rather than hunting it. As seen previously with eating washed-up marine life, scavanging doesn't count as predation.  
     Hence even these periods of land-based eating can't really be called 'land predation'.

Nature documentaries often tout that polar bears are the only animal that will purposefully hunt humans. 
     Yet this is documented out on the ice so it's not land predation. Even if polar bears did hunt humans on land, humans lack the blubber polar bears need to survive, so such a landbased diet would kill the polar bear. 
     Humans could only ever supplement the current marine diet of polar bears. One can't reclassify their overarchingnhunting stategy based on such a minor behaviour. To be land predators, land-based prey would have to be enough to sustain them (which it is not).
     Hence this doesn't make a compelling argument for polar bears being land predators.

Final Thoughts?

Polar bears are water-based hunters that hunt water-based prey. Thus choosing to describe polar bears as 'land predators' is completely off.