Cheap ass tyres are likely made of shitty hard rubber so can handle a bit more weight. A soild rubber tyre could handle even more, does that make it a superior tyre?
I have 84(pretty sure) on my car which consists of a pair of F1 GSD3 and a pair of RE002. Both tyres are bloody good. Would I got for a cheap as chips tyre because it can handle twice my cars weight? No chance. You're only talking ~60kg difference and when the weights are 487KG vs 545KG it's kind of pointless to compare.
I was in the same boat as you are. I just sold the mismatched tyres (by weigh rating only, both were GSD3 tyres) and got new ones (the RE002s). Problem solved.
Having different brands with different wear levels is a pretty good recipe for crappy handling. A matching pair of crappy tyres would rate better. With a matching pair of good tyres being the best option. IMO.