Piper is free to have and express his opinion about Arminians and exegesis, but it would be helpful if he would at least reveal which Arminian Bible scholars he has read and found wanting and why. Instead his response was merely dismissive and ought not to be taken very seriously—unless one takes whatever Piper says seriously just because Piper says it.
The concept of love (particularly how God loves) is a bit different on Calvinism. On Calvinism God loves the elect. Jesus died and rose again, for the few elect. This means that by definition, God as described by the consistent Calvinist is not omnibenevolent. Of course, a Calvinist could redefine the word “love” as it relates to God and claim that it is “loving” for God to allow those he loves to go to hell when they simply could not choose otherwise. In fact, this is the approach that many Calvinists take.
Even the idea of believing refers to individuals since only individuals can exercise faith; I do not see anything in the passage that would indicate that this “all” is restricted to something like all people groups, including some who can be saved. I do not think the passage even hints that this “all” is different from “all” including each person previously spoken of as under sin; of which “there is no distinction.” This understanding corresponds precisely with its usage before and in the following verses.
Two articles are added to the confession on singing hymns and the laying on of hands. More attention and information is given to the Lord’s Supper than Baptism. Baptism is affirmed for believers only through the church by immersion. The confession has similar understandings of salvation being a work of God in which He calls and provides grace to be saved. It is orthodox in its Christology and Eschatology. It differentiates between paedobaptism and New Testament baptism by believers.