My high-level math says without Nexen the west side wouldn't be any worse off than the rest of downtown. Give or take a few percentage points.
I think that only works if you assume the west end is a quite small portion of the total downtown office space, on the order of 5%.
Here's the math assuming 10% in west end:
45M sq ft total * 0.1 pct in west end = 4.5M sq ft in west end
4.5 M * 0.44 vacancy rate =1.98M sq ft vacant
West end excluding Nexen: (1.98-0.6 = 1.38 M sq ft vacant) / (4.5-0.6 = 3.9M sq ft total) = 35.4% vacancy
At 5%:
45*0.05 = 2.25 total space; 2.25*0.44 = 0.99 vacant
(0.99-0.6=0.39) / (2.25-0.6=1.65) = 23.6%, comparable to the rest of downtown.
(At 15% of the market, vacancy ex Nexen is 38.5%, and at 20% it's 40%.)
I don't know how much they consider the west end to be, but 5% seems low; my guess would be 15%. And of course, the vacancy rate anywhere else would be better if you ignored the single worst building in it.
It makes sense that even ex Nexen the west end would have higher vacancy rates; it has a lot of class B and C buildings, and I don't think any class AA ones.