Hello! your expert is 100% correct. There isn't an equation to convert degrees of rotation to a torque valve.
when a torque spec is given, for example, 90 ft/lbs, that value of "ft/lbs" is the resistance of rotation. Take three bolts: a rusty bolt, a new bolt, and a new bolt with oil on the threads. The rusty bolt will have the greatest resistance to rotation of the three, and therefore, will hit "90 ft/lbs" before the other two. The new bolt with oil on the threads will offer the least resistance, and therefore will require much more turning, to acheive the 90 ft/lbs. All this extra turning causes excessive clamping force, since each turn of the bolt brings the bolt head down lower. So if you torqued all three bolts to 90 ft/lbs, the rusty bolt won't offer enough clamping force, the new bolt will probably be just right and the new bolt with oil will be too tight.
When manufacturers give a rotation spec, they give an inititial torque valve (for example 10 ft/lbs) just to make sure the bolt is seated, usually very low. Then they give the rotation (180 degrees for example) because they know, that no matter if the bolt is rusty, clean or oily, that 180 degrees will give the same clamping force, no matter what.
If you don't beleive me, thats OK, its a hard concept to grasp. But google "torque to yeild bolts" and you will see a ton of information on the theory and benefits of using such, and maybe then you will understand the difference and why it can't be converterd.
I hope I helped and if you have additional questions, please let us know, we are happy to assist.