Three sections on ministers responsible for liturgical music. First, a few words about the psalmist. (Please don’t refer to this role as the “cantor.” It is not the same.)
102. It is the psalmist’s place to sing the Psalm or other biblical canticle to be found between the readings. To carry out this function correctly, it is necessary for the psalmist to be accomplished in the art of singing Psalms and have a facility in public speaking and elocution.
What is the function of the choir? Simple: to sing its own parts and to foster the singing of others.
103. Among the faithful, the schola cantorum or choir exercises its own liturgical function, its place being to take care that the parts proper to it, in keeping with the different genres of chant, are properly carried out and to foster the active participation of the faithful by means of the singing.[cf. Musicam Sacram 19] What is said about the schola cantorum also applies, with due regard for the relevant norms, to other musicians, and especially the organist.
The organist, too, and any other instrumentalist or singer exist mainly to render their own parts of the Mass and to foster congregational song.
104. It is fitting that there be a cantor or a choir director to direct and support the people’s singing. Indeed, when there is no choir, it is up to the cantor to direct the different chants, with the people taking the part proper to them.[cf. Musicam Sacram 21]
Without requiring a choir at every Mass (a difficult and demanding ministry stance, but not impossible) the Church gives an adequate set of preferences. If you don’t have a big choir, a small one will do. If you don’t have a small one, then a few singers. If not those singers, then a single cantor. It sets the bar for improvement just about everywhere. Speaking for my personal goals, I’ve always striven for a choir at every Sunday and holy day Mass. I haven’t always reached that goal, and I’ve worked for a pastor or parish or two who advocated the approach of all-eggs-in-one-basket. What about your parish?
Catholic Sensibility 
*Elevate the position of Cantor to the antiquated sense, ergo like Bach at Thomaskirche, Faure, Latona and Pascual, me at my joint, the poor schmuck with the pedigree at the top of a church music food chain, bereft and abused they may be, the Cantor is all things musical to all people at one church.
*The Cantor thus also coordinates choirs, additional choirmasters, accompanists/ organists, Psalmists, Songleaders, ensembles, etc. and their maintenance, scheduling and (ahem) training and catechesis! The Cantor may also actually be all or some of the above, including “choir” should s/he invest in an $800 primo vocalizer! (I know how you are about digital technology, but tacky as that might seem, it ain’t illicit! Rest assured, I’ve never even tried mine in 7 years!
*The ideal musical support system should focus upon achieving a “corporate” sort of participation, and in my estimation your preferernce for choirs overindividual leadership is also mine. OTOH, whether accompanied or not, a “leader” can function just as well from a place in the pews, unamplified, to take point on helping any congregation take up its singing role within the Mass or other liturgies. That same “song leader” ought to take that responsibility so seriously, if capable, to the more official duties of declaiming the psalm or gradual verses, and those for the Alleluia/Tract as well. Even beyond that, in truly enlightened joints, the Cantor could instruct either musical personnel (Psalmists, song leaders) or others towards the cantillation of the other elements of the Service of the Word, all the way through the Universal Prayer, if only to intone the response, if not the whole invocation (ala Good Friday.)
*If a parish has an enriched music ministry, then diversity both in repertoire and assignment should be also an expected and well-managed aspect the Cantor oversees and maintains.
*The one thing musicians, however striped, should not be held accountable for are the successfully sung responses to the orations canted by celebrants. Celebrants who subscribe and practice the notion that their own example of singing the processional hymns, or responsorials and such is the paramount of their assistance towards FACP are barking up the wrong tree. Getting these gentlemen to realize how important it is to cant orations with even a minimal efficiency is the best remedy for tepid PIP performance. Celebrants who rely upon organists to “bail them out” of canting, and then moan about poor participation are always going to be a day late and dollar short.
Thus endeth the rant. O Lord, we beseech Thee, Aye-men!