Complex sentence: Later on, McDaniel noted that THRUSH field agents were always doing stupid things and getting killed or arrested by U.N.C.L.E. agents--but THRUSH continued to exist and flourish, so there was obviously another group that was competent.
Split into simpler sentences: Later on, Mcdaniel noted that THRUSH field agents were always doing stupid things and getting killed or arrested by U. N. C. L. E. agents. But THRUSH continued to exist and flourish, so there was obviously another group that was competent.