There is absolutely no doubt that diesel powered buses are superior to gas powered machinery. And also, conversion from gas to diesel is grossly cost ineffective, unless you had the diesel engine for free, hundreds of hours to devote, and were a professional mechanic, fabricator, welder etc.
Speaking with 17 years in the bus business. about 100 buses and trucks, and having owned Cummins, CAT, IHC, Detroit 2 and 4 cycles, Deutz. Nissan. Ruggerini, Isuzu. Mercedes, Lister, Kubota, and probably a couple other diesel types that I've forgotten.
Gas buses have their place, and do well for infrequent use and shorter trips. But the fuel savings and longevity of the diesel make them the only choice for serious travelling, or industrial, serious applications.
Bus King of the Great SouthWest