While I do agree you can cut off some SP by turning off certain attributes, Fletchers attributes (or any attribute) no longer increase the SP consumption like mad like before, they are on a +10% modifier, so a LVL15 Crossfire is 13 SP more with the attribute on, it doesn’t really make that much of a difference sadly.
Also, what you said may be true for dailies and daily grinding, but not for ET for example, there you WILL throw those 5 Crossfires on every CD, the R8 meta Ranger or Sap2Fletcher3Mergen had nothing else, the build relies entirely on Crossfire spam/Broom Trap/Triple/DMA and unless you had a Falc3 in your group to benefit from, the SP usage is insane (even more with Chrono’s Pass) trust me, even full Solmiki I had to run around with Keistas for 31F and 36F… I even tried placing 200 SPR for the lulz during May2017 reset event but the difference wasn’t all that noticeable sadly… and I also had 200SP rec more from two unlucky (or lucky?) awakenings on gears. 
In the end, the SP usage on certain ranks is simply too high (and most of them being Archers build too) and with so little way of recovering mana, your SP micro-management is going to stress the hell out of you in certain situations. 