Sorry, but you make no sense. By your logic, any statement would be impossible to argue. You could say tomorrow that we could get a top 10 player and 5 first round picks, and I couldn't argue it, unless I call every gm that has a top 10 player to ask if he would be open.
As far opinion vs fact, we're talking about the future, so, by definition, everything is an opinion. Or, more precisely, a prediction.
That being said, I would definitely estimate the chances of Powell netting us a first rounder in a trade at less than 5%. At best.
As far as your argument about bad teams, they are weak because they are ignoring the fact those teams usually have cap space. The market this summer is going to be rough for a lot of good players. Guys like smartor Evans will struggle to attract 10m/year. That's why Lou settled for 8m this winter.
You are also ignoring the fact that teams know we have cap issues, they know we are not relying on Powell, and they can reasonably assume we'd be happy just to get his contract off the books.
You are also ignoring the fact that guys like evans or Lou couldn't be moved for a late first rounder - and Powell will probably never be as good as them.
And, finally, you are also ignoring the fact that Powell just sucks right now. At best, a team will be looking to buy low, if they were interested.