You made a sweeping accusation that replacement timing chain/components is common in cars today. The only "evidence" you provide is extended OCIs suggested by OEMs and some links to forums, because everyone knows that forums are representative of the owner base as a whole /s.
You didn't even have evidence of this "issue" from the same brand, let alone the same engine as the OP. Your claim of "extended oil change intervals" is off-based as Hyundai doesn't recommend extended OCIs. You have nothing to support your claim, yet you dig your heels in and demand to be proven wrong. That's not how this works. The burden of proof lies with the person making the accusation.
Also, you know for a fact that I can't "prove to you what caused OP's issues".. that's a stupid request to make. We don't even know what the OP's issues are because, as others have pointed out, Hyundais are sensitive to filters. If he's running aftermarket oil filters, those could very well be what his problem is.
Edit: And you seem to think that I think the timing chain is not the problem. It very well could be. My point was that the Gamma engine is not known for timing chain/guide/tensioner issues, so if that is in fact the problem, it is likely that some OCIs were missed by the previous owner. In that case, it would be prudent to run some short OCIs after the repairs to try to clean things up a bit.