I don't want to get into this "you answer my question first" mode. It's not very productive.
First, would you document your claim that early Baptists poured instead of immersed?
Second, Baptists consider themselves as New Testament Christians. The New Testament mode of baptism was immersion.
Third, Baptists were persecuted and killed for their views on baptism. Doing it the Bible way is not unimportant. In fact, the correct baptism is the mark of a true New Testament church.
Fourth, a disturbing trend in some Baptist churches is that they have decided exclusivity goes too far.
Before the rise of the Particular Baptists, there was no uniform mode of baptism among the first (original) Baptists, the General Baptists, they having been influenced to varying degrees by the Mennonites.
"The question of baptism by immersion before 1641 was a major topic of concern among the early Calvinistic Baptists. By 1641, adult baptism by immersion was becoming the prevailing practice for many Baptists congregations." This was taken for an article entitled "English Dissenters."
That is just one source, but it should suffice.
Baptists were persecuted and killed for their views on the subjects of baptism -- believers -- not on the mode.
I would agree that scholars agree that immersion was normally the New Testament mode, but when immersion could not be had, other forms were permitted. Consider the following from The Didache, a document first composed between 60-80 A.D. (with later additions):
Now about baptism: this is how to baptize. Give public instruction on all these points, and then baptize in running water, in the name of the Father and of the Son and of the Holy Spirit.. If you do not have running water, baptize in some other. If you cannot in cold, then in warm. If you have neither, then pour water on the head three times in the name of the Father, Son, and Holy Spirit.
It goes against the spirit of Jesus's teachings to take a legalistic attitude toward the ordinances.
I hold to believer's baptism, and I believe immersion most perfectly pictures the salvation experience and process, but I refuse to be pharasaical about it and exclude those who may have been baptized another way, especially since I don't believe that water baptism is necessary for salvation.
I could say more, but that's enough for now.