Both of the left two Talent routes in Frost DK require the usage of Pillar of Frost, which in itself is an optional talent. If its required for the talents to function but is not a required talent point, it should be a baseline ability, from a design standpoint. Either this needs to happen, or the two left talent routes need to be redesigned around something else.
For reference, the two talent lines which do not require Pillar of Frost to be obtain;
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Obliteration (While PoF is active X skills always grant Kiling Machine and a chance to generate a rune)
- Arctic Assault which follows, is significantly less effective without the optional point put into PoF.
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The other line ending with The Long Winter; While PoF is active your auto crits increase its duration by 1s up to a max of 5s.