Plenty of Saigas have come in with problems. They are effectionately know as "vodka specials". Gas ports drilled to big or too small, rails not aligned, bolt jumping, canted rear sight blocks, ...etc....etc. It happens.
Rifles put together from parts kits are every big as good as Saigas. The parts themselves are very good quality. How they are put together and by whom makes a difference. Guy with a hammer and a set of pliers is going to do a poor job. People often assume that because it's a simple design that it's simple to put together. It's actually quite the opposite. Where as the AR design is more complicated it's actually easier to put together. Try setting Headspace on an AK....not without a barrel pulling device or a dozen different bolts to try first. Getting those rails right is also a PITA! There are plenty of AK specific gunsmiths who build beautiful and correct AKs but they'll cost you some money. At least $500 for starters. Check out Two Rivers Arms. They specialize in Iraqi/Yugoslav AKs. Make excellent rifles, worth every penny. The owner by the way is Steve Russell a former Lt. Colonel in the United States Army and current member of the US House of Representatives from Oklahoma. That's just one example, there are many more like Mario from Piece of History firearms, In Range, and many more.
It's not enough to know an AK is an AK. There are many differences and difference in build and materials.
Pioneer from Poland is a commercial company. They make modern AKs on mostly new parts that THEY MAKE, not the military. Like any commercial manufacturer...price is the bottom line. So if the can cast something that should be forged or milled they will. If they can save mkney somewhere they will. Casting is fine for the most part if done correctly. Sometimes a defect happenes. As AKs go they are ok. They do also make rifles from military parts sources like when they imported the PPS43
There are worse companies and better companies. ..like it is everywhere with everything.
The design hasnt completely been exhausted yet. There have been a lot of rethinking and changing but like the US military, the Russian military also can't afford to dump their current issued rifles for something new.