i won't call 30 phones as "many" especially if you compare it to phones with QC3 tech
https://www.qualcomm.com/media/documents/files/quick-charge-device-list.pdf
and take a look at the charger list...
also... your "many 6 series" is not really many, and the 7 series are brand new to market and we are only just seeing phones with the 7 series SOC
617, 620, 625, 626, 632, 650, 652, 653, 665, 820, 821 are on QC3
630, 636, 660,670, 675,710, 712, 730, 835, 845, 855 are on QC4
I think the issue with the QC is that phone manufacturers, unless when you purchase their top of the line models, don't include the compatible charger during purchase.
this in turn gives end users that purchase a phone with QC4+ a dilemma; out of the box, i get a 10W charger, do i pay more to purchase a QC3 charger for an extra 5W of charging power? or should i pay even more for a QC4+ charger?
and honestly, with the battery capacity and power consumption of the SOC's, your phone should last a day's use. If your phone battery can't last a day, then you should take a hard look at your phone usage and learn to put down your phone more often for the sake of your health
No infact quite many phones from end of2017 onwards support qc4. 0 already.. Those sd845 phones and many 6 series and 7 series sd cpu.. Just that I believe many coy still see qc3. 0 potential and try to make it faster 27w,40w etc..