So? One voice alone can't save a dub. For example, Bleach had one or two decent VA's but the main characters VA was fucking terrible, and the scripting was awful (seriously, translating reiatsu literally into the words SPIRIT PRESSURE?) so the dub overall was absolutely abysmal.
So yeah, Mugen was pretty good but the rest of the dub was either meh, or bad (Fuu is SO obnoxious-sounding).