Yoshua, I know other responses to these have been given, and I think there's too many points of disagreement for me to cover all of them at once, but I'd like to offer a few critical comments on several points I think are interesting.
1. "Spiritual Formation" as a movement appears to be a straw-man
All of these articles seem to be concerned with some particular movement called "spiritual formation". I'd never heard this term before, and am unaware of this movement. I think it should be pointed out that making this particular movement stand in for the entire possibility of Christian contemplative practice is a straw-man, in a way that dealing with mainstream Catholic or Orthodox views would not be. Lets say there is in fact some objectionable point of practice in this movement (or any other), even so it would be fallacious to present that as a refutation of Christian contemplation in general. I'll try to make this point more concrete in responding to some of the specific objections raised, but it would be like if I were to suggest the entire body of reformed theology dealing with soteriology was unbiblical and non-Christian based on an objection to the way sanctification is explained in some particular modern western popular work.
In a similar way, the Christian Research Network definition of "contemplative prayer" is certainly biased. It picks sources to criticize but those sources are not really representative.To pick one example, it presents "repetition of a mantra" as a core practice of Christian contemplation. The use of the word "mantra" is certainly intended to pejorative, an implication of suspicious eastern roots in the mind of the reader. Personally, I do not think it untoward for modern Christians to borrow terms like mantra if they find them meaningful, and the relation between Christianity and other religions is a more complicated topic. But, if the argument is about contemplative prayer in Christianity, the problem is that no traditional Christian descriptions of contemplation use the word mantra. Even where there are at some surface-level similarities between (say) the Jesus Prayer of hesychasm and japa in Hinduism, they are certainly not equivalent. It's therefore disingenuous to refer to "repetition of a mantra" as a central practice of Christian contemplation. Most of the other objections are similar. For example, no eastern orthodox practitioner of contemplative prayer would disagree that "prayer is ultimately a form of worship. It should glorify God alone."
2. Dealing with the question of a "biblical basis" of practice or of mysticism
As others noted, MacArthur doesn't elaborate on
what the true biblical paradigm is, but given his list of terms at the beginning of the video (justification, sanctification, glorification) and his background, it seems reasonable to assume he is referring to a protestant framework of soteriology, and I think there's a point to be made here that doesn't depend on narrowing it down further.
The other quote says that advocates of contemplative prayer appeal to ancient monks (or elsewhere, the Desert Fathers of the 3rd century) rather than the Bible. However, there is a parallel. MacArthur's claim to a "one true biblical paradigm" appeals to 16th century writers, i.e those of the reformation. What I mean is this: As a systematic, conceptual framework, reformed soteriologies which use terms like "sanctification" and "justification" in a technical way, don't exist as such in the Bible. Both the terms and their understandings are derived from an interpretation of biblical texts, but as a coherent whole they certainly say more than the text does directly. There is no conceptually univocal and systematic theology of justification in the new testament. Later Christians, like the reformers, provided the systematization.
In an analogous way, advocates of contemplative prayer in the ancient Christian traditions, for example Evagrius of Ponticus or Gregory Palamas in his defense of hesychasm, were systematizers whose frameworks are based on biblical texts. If you reject contemplation because it is not contained in a systematic way in the Christian scriptures, than you should also reject reformed soteriology for the same reasons. Or, if you allow for reformed soteriology as a 16th century systematic formulation of biblical principles, it is possible in a similar way to allow for contemplative views on Christian practice as 4th (or 7th or 12th or etc) century formulations of biblical principles.
This gets back to the argument about hermeneutics, and so to reiterate: it is logically invalid to claim for reformed soteriology a biblical status if, in order for a view to be "biblical", it must be contained word for word in the biblical texts. Neither sola scriptura, nor the reformed concept of sanctification (with all its deductive corollaries) exist as such in the biblical texts. Nor does hesychia as a practice of Christian contemplation. But both are derived from a meaningful human engagement with those texts.
To present an insufficient introduction to an orthodox Christian systematization, see the first parts of this document, which excerpts from a book on eastern orthodoxy spiritual life called "The Orthodox Way":
http://www.clarion-journal.com/files/orthodox-contemplation-2.pdf
Whether dealing with the Pseudo-Dionysian model of
purification, illumination, and
union, or Maximos' categories, all of these are formulated in reference to the scriptures explicitly, following similar models of exegesis (roughly) as the reformation, as far as being based on biblical texts. It's also worth noting that every ancient Christian writer on mystical theology and Christian contemplative life puts purification and repentance as a primary stage. One of the criticisms offered about "spiritual formation" in all of these articles is that supposedly these mystical practices dispense with an emphasis on sin, but that's simply not true of any authentic historical Christian contemplative practice. You might see also something like The Ladder of Divine Ascent by John Climacus.
I would like to respond further to a few points but this is long enough for now and I'm out of time.
The adversary of God is also my adversary.
