all that you said is correct. what you fail to realize is, the oem spring sits in special designed cups in the lower control arm holding up your vehicle at ride height. you can remove your factory shocks and the height will not change, they are only there to stabilize the spring action. however, if you remove the spring and leave the shocks, your truck will sag proving the weight is on the oem coils.
when you bolted that coilover on, your frame weight is on the top of the coilover spring but the bottom of that spring is sitting on the coil adjuster, which in turn is pressing on the two attaching bolts. all of the front vehicle weight is on those two bolts per side.
you loose. coilovers on a stock control arm is completely unsafe. you would need lower arms designed for coilovers instead of coils..