Can we trust Isnad?

Traditionalists believe that because a Hadith has an isnad that, therefore it must be authentic, but again, there are a lot of problems with this kind of reasoning. The most notable is that there is no guarantee that the isnad is valid. This is because people have been fabricating isnad just as rampantly as they were fabricating Hadith.

6:19 Say, "Whose testimony is the greatest?" Say, "GOD's. He is the witness between me and you that this Quran\ has been inspired to me, to preach it to you and whomever it reaches. Indeed, you bear witness that there are other gods\ beside GOD." Say, "I do not testify as you do; there is only one god, and I disown your idolatry."

(١٩) قُلْ أَىُّ شَىْءٍ أَكْبَرُ شَهَـٰدَةً قُلِ ٱللَّهُ شَهِيدٌۢ بَيْنِى وَبَيْنَكُمْ وَأُوحِىَ إِلَىَّ هَـٰذَا ٱلْقُرْءَانُ لِأُنذِرَكُم بِهِۦ وَمَنۢ بَلَغَ أَئِنَّكُمْ لَتَشْهَدُونَ أَنَّ مَعَ ٱللَّهِ ءَالِهَةً أُخْرَىٰ قُل لَّآ أَشْهَدُ قُلْ إِنَّمَا هُوَ إِلَـٰهٌ وَٰحِدٌ وَإِنَّنِى بَرِىٓءٌ مِّمَّا تُشْرِكُونَ

To put in perspective the number of inauthentic Hadith that were in circulation during the Sahih compilations in the 3rd century Hijra, Bukhari himself claimed to have written over 10 million Hadith and memorized the chain of every single one. As absurd as this claim is, he also claimed in the same excerpt below that he struggled to remember the names of his relatives.

The compilations of Kutub al-Sittah began around the year 850 CE. If we look at the respective compilers, we see that they went through hundreds of thousands of Hadith and determined that ~99% of the hadith they reviewed were either not Sahih, according to Bukhari or Muslim, or failed to even rank as Daif, according to the other compilers.