I understand that many have different opinions about the statement "Initial evidence of the Baptism of the Holy Spirit is speaking in tongues." I have been fellowshipping with brothers and sisters who do not agree with that statement for 40 years. It is not a deal breaker or a point of contention with me.
The Assemblies of God being about 70 million I find to have the best doctrinal interpretations of all other Pentecostals groups and I believe that God is behind the rediscovery of these doctrines that swept the world in the early 1900s and really started with an attempt to answer the question "What does the scripture say is the evidence that one has been baptized in the Holy Spirit?" The answer to that question was presented to a Bible College in Topeka Kansas and all the students came up with the same answer. The gift of speaking in tongues.
They began to pray earnestly for the this Baptism of the Holy Spirit and received it by faith and were given the gift of tongues. Then they began to preach it and the Azusa Street revival which started on the front porch of a house on 216 North Bonnie Brae and then moved to an old church/factory/barn on Azusa street was instrumental in spreading the message world wide. Of the many pastors who experienced that baptism of the Holy Spirit at that time about 300 gathered in Hot Springs Arkansas in 1914 the Assemblies of God was started and now has about 380,000 churches and still growing. It is the fastest growing denomination and the largest Missionary organization of all evangelical denominations.
There is a group called United Pentecostals in Christ who teach that you have to speak in tongues to be saved and if you got baptized in water in the name of the Father, Son and Holy Spirit you have to do it over again in the name of Jesus or you are not saved. The UPC is an embarrassment to pentecostals and many don't like to say they are pentecostal and use the word Charismatic instead because they don't want anyone to think they are part of the UPC cult.
I agree with you that Paul said to desire both gifts but that prophecy was greater. The point that is often stressed in doctrinal statements among Pentecostals is that the speaking in tongues appears to be the initial gift and common for all who first experience the baptism of the Holy Spirit.
Many of today's pentecostals are practicing the "fake it till you make it" with tongues because tongues is the easiest gift to fake & most of their "interpretations" are so positive they could have been copied from Lakewood Church. Tongues is used also because it edifies self above all other gifts. It's become the "I've got it therefore I've arrived" attitude. In the modern church, those who use such fakery becomes a false prophet & will receive a false prophet's judgment.
I don't mean to sound like a killjoy, but it's just that bad, & getting worse because we are so close to the tribulation.
The predominant thing in the Pentecostal movement is the Falling Away, just as it is for every christian denomination.