Having worked in a fabric store, your complaint is familiar. It sounds about right that your measurements really are closer to size 6, when you purchase a 2.

One part of a pattern envelope that's frequently overlooked is the part that charts the actual garment measurements. The chart usually is on the back of the envelope, beneath the yardage requirements. If it's not there, it should be on the first page of your instruction sheet. I've faced that sizing frustration many times -- I haven't been able to figure out why commercial manufacturers and pattern companies can't coordinate their standards.

When you're selecting a pattern size, choose first (but don't buy it yet!!) on the basis of your body measurements. If they fall in different sizes, keep in mind that the bust measurement is the hardest to alter, so choose what's closest to your measurement. Loose-fit, semi-fitted, etc. affects the actual garment size. Once you've chosen a pattern size, look at the actual garment measurements and change your size accordingly. Check this Threads article again for ease standards -- the actual pattern size you need may be closer to the measurements of a purchased garment.

Each pattern company uses slightly different slopers (original basic patterns from which they create the new designs). For example, I've found Butterick has a relatively high bust point -- they gear their patterns for younger, slenderer (if that's a word!) bodies. That's good news -- lets you know how you need to adjust the pattern if you absolutely fall in love with one of their designs.

I hope this helps! It's made a big difference for me.