The Incarnate God-Man, Christ Jesus Our Lord, had an answer for their question.
The "reformers" do not, and never will. "Lest the Lord build the house, the builders labor in vain."
Rather, the Lord and His church established their claims - which manifestly did not include such things as praying to the departed or ostentatious clothing and titles (not even being distinctively titled "priests") - upon Scriptural substantiation, as that is what is abundantly evidenced to be the transcendent material standard for obedience and testing truth claims.
And it is the historical evangelical gospel which effects manifest regeneration, testifying to the church as the body of Christ being that of the living God, (1Tim. 3:15) versus its institutionalized counterpart overall, of which Rome and many Protestant churches are part of.
As for the work of the Reformers being "in vain," instead you could be thankful for the impetus they provided toward Rome's own reforms, but above all for the multitudes that have been added to the kingdom of God thru their preaching which convicts souls of of their damned and destitute desperate condition, and directs them to lay hold of the risen Lord Jesus for salvation by His sinless shed blood, and so follow Him . And evangelicals yet evidence more of than Catholics overall (though both as in overall decline).
For to be truly in vain then no good fruit could be allowed, but as Rome affirms that properly baptized Protestants have the Holy Spirit, and are part of the general body of Christ, and (according to PJ2) even have saints, then you must allow that their work has not been in vain.
Or are you are part of the SSPX sect or sedevacantist schism, if you do not mind me asking?