but I found pilot reports that not feathering the bad engine was only marginally worse.
is simply bull$hite ESPECIALLY when close to VMCA. With 4 blade props feathering is essential not only for climb performance but to maintain controlability... if this unfortunate pilot has gone below VMCA (maybe autofeather u/s or not switched on) his chances were slim.
Forgetitng to retract the gear gives less of a problem than not feathering. Just reduces your rate. Given the location (having been in the same building umpteen times) IŽd say it very much like a classic loss of control, airplane turning left with ever steeper bank.
The 3 blade version was way more forgiving in the same scenario, thats why Autofeather is mandatory on anything with more than 3 blades on a B200.
With full fuel and one pilot modern B200 are very close to MTOW.