BS”D
Yes – yshua is the name that they use but it could be a construct of the j4j. It is not even clear that this guy existed and if he did that the religion has anything to do with the (rather minor) historical figure that may have been.
Also, if not the X, what should we use? I know the X is theoretically wrong but it is what everyone uses. If we use the word then we are saying oiso ho’ish is hristos, or the anointed one which is lehavdil an exact translation of Moshiach. Maybe we can use yoshkeists or yoshkelach on this board…