I agree that telling people "sim yourself" without any context or manners can be rude and unhelpful, but it IS usually the correct answer for most questions where it is applicable. DPS is a math calculation, and simcraft is a calculator. There are factors at play in real practice that make target dummy sims less useful as a measurement; but there are options within the program that you can set to account for those discrepancies.
When it comes down to it, every character is different (this expansion more so than ever, because BiS doesn't exist because of titanforging), so giving you the EXACT right answer is often impossible from a forum post or an armory profile (as most players carry multiple pieces in their bags and changing out pieces to try out multiple configurations). Telling someone to sim them self is the WoW equivalent of "teaching a man to fish so they don't go hungry again".