Not that much has really been learned or uncovered. The discovery of codex sinaiticus in a Catholic monestary; and codex vaticanus which was stored in the Vatican library. The fact that both of these have Catholic connections should make a person suspicious right out of the gate.
The "expert scholars" are Constantin von Tischendorf, Henry Bradshaw, Fenton John Anthony Hort and Samuel Prideaux Tregelles. These are the ones we trust when they tell us that sinaiticus and vaticanus are the oldest and most reliable manuscripts available. But these men are anything but experts and shouldn't be trusted without first looking into the opposing side. There are always two sides to everything.
I am speaking about the science of translation in general.
Not the different manuscripts being used to translate but the decision as to why a certain Greek word should be translated into a certain English word.
There are cases where a Greek word occurred only once in the NT and there are no known contemporary examples of that word in other documents from the first century.
We have discovered documents where some of these words were used and this helped confirm the best English word that should be used.
We have learned a lot since the KJV translation.
But most importantly when discussing why NIV, ESV, CSB, NASB might have slight differences in wording from the KJV one must consider the challenges of translating from one language to another and especially ancient languages into another. There will be slight differences of opinion even if they are working off the same manuscript and one must read the explanations of the translators to understand why.
This making a big deal about slight differences in English words from one translation work to another is not a conspiracy or a matter of evil motives.