I encourage everyone that has not learned general linguistics, some Hebrew and Greek to invest 2019 into basic courses on linguistics, Hebrew and Greek. There are so many free courses and low-priced books out there on the Internet today, that it's unbelievable. But, there is also unreliable information. I highly recommend that you all read highly reputable, recognized scholarship. That doesn't mean that it's all flawless and that they never contradict each other, but that it's recognized scholarship. Go check Logos.com. These kinds of questions are easily answered by reading through a very small introduction to Hebrew and Greek grammar, which includes the usage of the "kai" conjunction.
First, I recommend that you all start using biblegateway.com. In there, you can put the passage in question and then you can click (just below the translation) on " Colossians 1:29 in all English translations." It will then list almost, if not all, English translations and revisions in existence. It's astonishing that people heavily continue to use the KJV and its editions and revisions, and barely mention or reference more up-to-date and more reliable translations such as the ESV, ISV, NET and LEB.
Second, I recommend that you all start taking advantage of the NET Bible and its translation notes. Yes, the NET Bible is free online and it includes translation notes by the translators. It's not flawless, but it's scholarly and extremely useful.
Third, I am not a grammarian ( although I've done 1 full year of Hebrew and Greek grammar, including summer time ), so I cannot myself explain in detail how the "kai" conjunction is used in the NT and outside the NT. Therefore, let me simply make some references here that should answer your question...The simple answer is that the "kai" conjunction is not always necessary to translate, and it's sometimes not even translated in certain other passages even by supposed "literal" translations such as the KJV. Also, "kai" can variously mean different things, it does not always mean "and" ( this is the impression you give us ).
There are dozens of really excellent Greek grammarians out there, some being Dr. David Alan Black, Buist Fanning, Steven E. Runge, Prof. Stanley E. Porter, Prof. Emeritus Chrys C. Cargounis, and others. There is another one : Dr. Daniel B. Wallace. He " founded the Center for the Study of New Testament Manuscripts (CSNTM) to utilize emerging technologies to preserve and study Greek New Testament manuscripts. " Please, look for Dr. Daniel B. Wallace if ever you want to know something about greek or about NT Greek Manuscripts.
http://www.csntm.org/About/WhoWeAre
https://danielbwallace.com/cv/
https://danielbwallace.com/about/
https://danielbwallace.com/2012/10/08/fifteen-myths-about-bible-translation/
Now, let me quote Dr. Daniel B. Wallace in one of his grammars:
On Ephesians 1:1, he says:
It is probable that here the Greek conjunction “and” has the meaning
of “namely.” It serves the purpose of explication and may therefore
occasionally be omitted in translation if its intent is preserved
Daniel B. Wallace, Greek Grammar beyond the Basics: An Exegetical
Syntax of the New Testament (Grand Rapids, MI: Zondervan, 1996), 282.
On 1 Cor. 2.10, Dr. Wallace shows that "kai" should not be translated "and", but "even" (i.e., "kai" --> "even"):
τὸ πνεῦμα πάντα ἐραυνᾷ, καὶ τὰ βάθη τοῦ θεοῦ
the Spirit searches all things, even the deep things of God
Daniel B. Wallace, Greek Grammar beyond the Basics: An Exegetical
Syntax of the New Testament (Grand Rapids, MI: Zondervan, 1996), 671.
...And there are many more examples where "kai" is used in various ways, either because of the Koine Greek language itself or because of the author himself, to produce different kinds of conjunctions and some are not translatable.
Just one last citation from another grammarian, Dr. David Alan Black:
iii. Greek does not have a conjunction meaning “both.” Instead, καί is
used, as in εἰμὶ καὶ υἱὸς καὶ δοῦλος, “I am both a son and a servant.”
καί may also be used adverbially, in which case it is translated
“also” or “even.” Compare Matt 10:30: “But even [καὶ] the hairs of
your head are all numbered.”
David Alan Black, Learn to Read New Testament Greek (3rd ed.;
Nashville, TN: B&H Publishing Group, 2009), 31.
Translation philosophies or methodologies:
https://en.wikipedia.org/wiki/Dynamic_and_formal_equivalence#Bible_translation
https://blog.logoscdn.com/wp-content/uploads/2016/05/image00-620x250.png
https://blog.logos.com/2016/05/bible-translation-best-good-ones/
Conclusion
The conjunction kai for this particular translation of this verse is not necessary. If you've done Greek, or you are a Greek grammarian or a translator, you may have your preferences, but it's not correct to insist that omitting the "kai" in any particular translation of this verse is wrong. It just isn't.
