KenV They had essentially zero air-to-air capability
melmothtw beat me to it. The F-105 was credited with 27.5 kills (most with the gun) with what was essentially designed as a single seat penetration bomber is no slouch. That's more kills than other attack/bombers such as the A-4, A-7, A-6, and even the fighters such F-8, F-100 etc. Of the Western aircraft only the F-4 got more air to air kills in Vietnam/SEA. If you believe all the reports, the B-52 had the "best" air to air kill ratio.....
This study
http://www.dtic.mil/dtic/tr/fulltext/u2/c016682.pdf is a good read on losses by type and with some good nuggets. Interesting about the part of the F-105's ability to "die slowly", which gave the aircraft perhaps an underserved rugged reputation, but highlighted that the abiltiy for an aircraft to fly on for even just a bit was a big factor in crew survival rates.
Yes the Thud had a high loss rate, perhaps 390 (sources vary), but the vast majority of the losses were to AAA, then SAM's then another big drop to MiGs, with perhaps 20+ lost to MiGs. So perhaps a 1:1 ratio, and many more likely survived by the Thuds impressive ability to outrun the MiGs down low.
As for the vs. F-35 debate, agree with the others. Bomb load, range and speed goes to the F-105, but the electronics and other feature is no comparison. Apples and oranges. Heck a B-24 could carry a similar bomb load farther, but no one is suggesting we should re-open the Liberator production line.