The majority of scholars who weigh in on the subject, whether they are religious or not, believe that Jesus of Nazareth was a historical person. Judaism tends to agree.
I don't know anything beyond this personally, but I do know that the Gospels, from a critical Christian take, are not viewed as 100% historical. They can't be as none of them agree with one another.
There are things in the Gospels that even Christian scholars know are not historical. This is just one example.
Matthew chapter 21, the famous and most important triumphant entry into Jerusalem by Jesus, celebrated every Palm Sunday by Christians, read as follows:
When they drew near Jerusalem and came to Bethphage on the Mount of Olives, Jesus sent two disciples, saying to them, “Go into the village opposite you, and immediately you will find an ass tethered, and a colt with her. Untie them and bring them here to me. And if anyone should say anything to you, reply, ‘The master has need of them.’ Then he will send them at once.”
This happened so that what had been spoken through the prophet might be fulfilled:
“Say to daughter Zion,
‘Behold, your king comes to you,
meek and riding on an ass,
and on a colt, the foal of a beast of burden.’”
The disciples went and did as Jesus had ordered them. They brought the ass and the colt and laid their cloaks over them, and he sat upon them.--Matthew 21:1-7, New American Bible, official Roman Catholic Version in the USA.
The footnote to this reads, in part:
Isa 62.11; Zec. 9.9. The ass and the colt are the same animal in the prophecy, mentioned twice in different ways, the common Hebrew literary device of poetic parallelism. That Matthew takes them as two is one of the reasons why some scholars think that he was a Gentile rather than a Jewish Christian who would presumably not make that mistake...[painting] an awkward picture resulting from Matthew’s misunderstanding of the prophecy.
Note also the famous Beatitudes or Sermon on the Mount:
“Blessed are the poor in spirit,
for theirs is the kingdom of heaven.--Matthew 5:3.--NAB.
The footnote reads, in part:
Although modified by Matthew, the first, second, fourth, and ninth beatitudes have Lucan parallels. The others were added by the evangelist and are probably his own composition....Matthew added "in spirit" in order either to indicate that only the devout poor were meant or to extend the beatitude to all, of whatever social rank, who recognized their complete dependence on God. --NAB.
So while even present-day Christian recognize that the Gospel writers added traditions to their writings that did not originate with Jesus, does this mean Jesus was "just a preacher like Charles Russell" as you put it?
No. While Jesus is not recognized as the Messiah by Jews, he is recognized as a great Jewish teacher, otherwise known as a Jewish Sage.
In December of 2015, the Orthodox Rabbinic Statement on Christianity said about Jesus, in part:
We acknowledge that the emergence of Christianity in human history is neither an accident nor an error, but the willed divine outcome and gift to the nations....Rabbi Jacob Emden wrote that “Jesus brought a double goodness to the world. On the one hand he strengthened the Torah of Moses majestically… and not one of our Sages spoke out more emphatically concerning the immutability of the Torah. On the other hand he removed idols from the nations and obligated them in the seven commandments of Noah so that they would not behave like animals of the field, and instilled them firmly with moral traits…..Christians are congregations that work for the sake of heaven who are destined to endure, whose intent is for the sake of heaven and whose reward will not denied.”
Russell's work did not effect the nations as did that of Jesus' of Nazareth.
Did Jesus feed thousands with a few fish and a loaves of bread? Did he walk on water?
I don't believe in the supernatural. A lot of Jews are like me who don't believe in a God that breaks the laws of nature and supernaturally gives his sages and prophets abilities that amaze and bewilder. If there is a God, why do you need a miracle? Isn't the world we live in and the starry heavens enough proof for you?
But I am not here to judge. The Gospels may be stories like our Jewish myths that are meant to teach lessons, not report on history. Too many people might have lost the point of the Gospels and attribute to Jesus the wrong things. That would be a shame.