Freewheel wobble can be caused by poorly machined threading on both or either the hub or the internal thread of the freewheel and the wobble can be slight to huge. In my experience older freewheels and hubs made for high end bikes before freehubs were normally accurately machined but nowadays freewheels are purely a budget offering and built to rough tolerances. However that said you should still be able to make the adjustments so gear changing is accurate it's just the adjustments are more critical than a freehub drivetrain. That is one of the big issues in that the cheap bikes need if anything the most skilled bike mechanics but people buying cheap bikes are often the most casual cyclists who lack those skills. When you buy a quality bicycle you can pretty much throw it together and ride within 10 minutes of opening the box but again a cheap bike might need a full service and adjustment before it rides well which could be a few evenings work. I guess my point is you have to up your game when dealing with freewheels and they aren't as easy to setup as a decent freehub based drivetrain especially if you have an example with excessive wobble.