I've used many different brands of 5.25", 8", and 3.5" floppy and minifloppy disks and the ones that always seemed to vary in quality were the Verbatims (5.25" and 8"). in 3.5" disks, the quality in general was never as high as the larger sized disks, and I have had many more failures that I ever did with the larger sizes, including just about all brands. At the begnning, the quality was uniformly bad, at the end, it was much better (5.25" and 8"), and sometimes with the consolidation of manufacturers, you didn't have a choice when buying.
Platinum was a relatively late brand coming to market, launching in 1982 with 5.25" minifloppy disks in 48tpi. I remember them because their promotion offered to Seller for signing up to sell their brand of disks was a complete boxed reproduction set of the Original Beatles Albums on vinyl. I was working as the Assistant Manager at the Heathkit in LA when the Platinum Brand was introduced. In charge of Non-Heath Products, and Inventory for the whole store among other duties, I was the one at the store that controlled the product mix and inventory of producted marketed and sold by the store. The Promotional Set of Beatles Records were produced by Sony without any marking on the jacket, sleeve, or record that I ever saw that would standout, marking them as reproductions. Very High Quality, I still have the set I got when I was working at the LA Heathkit in around 1982.
The initial floppy disks very very high quality and the box was heavy and better designed than other brands. Later, the actually disk and boxes got cheapened. If you had problems with Platinums, I would expect that they were the later production ones. The ones I bought were marked DSDD, and were 48tpi, but I have used them for everything up to 1.2mb, and they still work perfectly to date. In 30 years of use, I've only thrown away one as defective (and that was over 20 years ago).