300K is more than double the current Russian forces. This means that Russia wants to have more than Donbass, 100%. My guess always has been Odessa. It is 10x more valuable than Karkow.
200K alone is more than sufficient to capture Donestk, just not within a timeline that satisfies Russian nationalists or Putin (i.e., too slow of progress, too slow at this rate of progress)
500K is just right amount to capture Donestk, on a satisfactory timeline, aligned with original expectations in terms of speed (i.e., "
Donbass conquered by August" by some users).
Odessa and Kiev? Even with 500K troops, those targets would drag out the conflict for many more years. It remains to be seen if Putin can sustain a prolonged conflict, but this partial mobilization move seems to indicate he has urgency to end the conflict as soon as possible. If it was political expedient to drag this conflict out forever without mobilization, he would have done just that.
I predict 500K troops will be a rapid end to Donestk, Putin unilaterally declare victory, and annex the damn place. Putin quickly end of mobilization, then engages in decades long border skirmishes like Sino-Vietnam (1979-1991).