Problem with µ43 45mm 1.8

I don't have that lens but your results don't surprise me. Many lenses are reported to be much softer wide open - not just a little - and are more prone to ghosting/CA etc.  I've never heard of a lens that was as sharp wide open as it is stopped down, although some come close.

Some very fast lenses are optimized to be the sharpest lens possible wide open but aren't as good at f/8 as other, cheaper lenses. They're still soft when wide open but it's just that they're not as soft as other lenses. The $120 "Nifty Fifties" 50mm 1.8 lenses from CaNikon are reported to be sharper at f/8 than their much more expensive f/1.4 and f/1.2 brethren. But they aren't as sharp at f/1.8 as the faster versions. The more expensive lenses were designed with the understanding that f/8 performance isn't as important as f/1.4 performance, that those specialty lenses were going to be used mostly wide open.

That's not to say your copy isn't off. It could be. You found it was a lot softer wide open than stopped down, not just a little. You also found it was more prone to purple fringing, ghosting, etc. That's true of many, many lenses. So the jury is still out on your copy.