I for one have no problem in recognizing that he achieved the goals set for him. At a high cost.
No matter what the doctrinal situation in the country is, I just can't personally see such a waste of manpower as a sign of a great leader. In my book it more is an example of the mentality and sense of duty on the part of the actual men fighting, not brilliant leadership.
As such, I'd rate for example the aforementioned Bill Slim higher in this comparison. Easily.
While I admire your humanism and as a former member of the military would hope to have commanders who also value the lives of their soldiers there are a few problems with your statement. One of the jobs of a military commander is to achieve the assigned objectives. In most cases achieving the objective will result the deaths of some of his men but the assigned goal is to achieve that objective. The role of the commanders is to trade lives for "objectives" as efficiently as possible but rarely can you achieve an objective in war without losing lives. Yamashita's objective was to defend the Japanese home islands by carrying out a war of attrition which would prevent the transfer of US forces from the Phillipines to the home island invasion force. In addition, the prolonged campaign caused over 47,000 combat casualties for the US and another 93,000 non combat casualties (fighting in jungles and mountains is not good for your health even if you don't get shot or blown up) that for the most part were more or less permanently unavailable for the invasion of Japan. By the end of the war there were still 115,000 Japanese soldiers in the Phillipines opposing a significant American Army (the 6th Army was slowing transitioning to an invasion force for the home islands but was being replaced by the 8th Army). The US Army's evaluation was that by March 1945 the campaign was won but.... (they still had to have many more than 115000 men in the Phillipines because of Yamashita) (www.history.army.mil/brochure/luzon/72.28.htm) The US Army thought Yamashita could have fought more actively and maybe caused a few more difficulties and possibly combat casualties but admits that that would have meant fighting in open terrain around Manila and central Luzon against overwhelming US superiority in armor, artilllery, supply, air support etc and that if they did so the campaign in the Phillipines would really have been over much more quickly. (possilby with a few more combat casualties but a lot less non combat casualties).
Yamashita obviously didn't see it that way. What Yamashita did was correctly evaluate a strategically hopeless situation and make the most out of it which I think is the sign of a superb leader and commander. In modern warfare commanders rarely get to pick their wars or strategic situations they have to play the hand they are dealt.