Hi TZ,
Sorry I'm late.
I disagree with some statements made above, but any one person's experience will be different from anyone else's.
I have gone the other way: Inventor to SW. Also struggled (and still do somewhat) in the same way you have.
There is still a long list of things that I could do in Inventor that I still cannot do in Solidworks.
There are strong points in SW that I don't use or care about; another reason why my complaints would not matter to another engineer.
Here are some other thoughts:
I use CAD in a particular way. Less "export to CAM/FDM" and more "Print on paper" and "very detailed process-dependent instructions". It's the way my industry works in my area on the kind of projects I do. It's not everyone's cup of tea.
Sharing my experience in the transition has been helpful.
You asked some specific questions:
Are there certain design functions that simply cannot be done in Inventor because it is a lesser expensive program?
There are constraint types that are unique to each program. You can accomplish the same, but the notion of "insert" does not seem to exist in Solidworks. When you're introduced to the differences you will be tempted to say "so what" or "big deal" but there are other differences in the workflow that increase the power and speed of use when you become more skilled.
Are more advanced features such as lofts, curve-driven sweeps, and the like easily doable in Inventor?
Absolutely, and I'm comfortable with them in SW already. The modeling transition is not the hard part.
If, at this point, you are thinking "what else but modeling?" then you use 3D parametric CAD in a very different way than I do.
What about structural steel and sheet metal, as in does Inventor easily bend and unbend sheet metal pieces?
Same as above. Also just as easy to pick up.
Does Inventor offer an FEA add-in like SW Simulation, or does it require a separate program?
Yes, of course. I think it's expensive however.
How easy/difficult is the assembly process in Inventor, and what about top-down design?
Equally easy for a person who has mastered each software to an equal level.
Your real obstacle, if you have already mastered top-down design, is teaching it to people at your new company in software you are not intimately familiar with. In that situation, you know a particular philosophy that can be used, but not the method in the new software. Depending on the
imbecility experience level of the CAD jockey whose hand I am attempting to guide, I have found it difficult to express concepts of top-down design when I can't properly name all the steps.
My overall feeling is that Solidworks is easier to learn, but it is optimized for users with limited skill. When I attempt advanced modeling or drawing techniques with SW, I get bogged down in tedious menu mazes because the workflows cannot be streamlined.
Inventor is harder to learn, hence more frustrating for some, but once you get over the hump, you can increase your skill and it keeps delivering efficiency that SW can't.
Make absolutely sure that you find, use, and become proficient with the Inventor PRODUCTIVITY TOOLS. As many of them as you can.
So if you ever do make the career switch, be confident that you can probably meet expectations quickly.