What was Miandad like a catcher? I'd like to factor that in more than I do but I don't know enough about how good a lot of players before my time actually were at it.
He pops up a fair bit in score cards, especially to Imran, but never referenced with regards to his aptitude. His catch ratio is also not the best. He's not in my top 30, but that's not definitive, and sadly yes I have one of those, and I should also explain how they are formed.
For the ones well before our time, I first read through bios (like on Cricinfo for Barlow and Bruce Mitchell), then read up on everything you can about them. When you're in that tier, it tends to be mentioned along with batting or bowling exploits. The catching ratio tends to support to some extent. Also reading up on any and everything you can find on the top lists from those eras.
For players of more modern eras (and that's including everything from the 60's) there's video evidence to support those claims. But again you scour the lists and for specific mentions. So it's bios, references, lists, stats and video evidence. The mentions and catch ratios basically prompts further research.
Guys like Hammond, Simpson and Sobers are locked in, there's as much spoken about them for their fielding as anything else, along with Mark they possibly make up my Mount Rushmore. Of course for Hammond there's the possibility of hyperbole, but he seems to have been universally acclaimed and accepted as the early GOAT. Sobers, there's lots of examples of spectacular catches, falling forward for the low fast ones of Hall and Griffith, the diving ones to the side and everything in-between. He made it look so damn easy. The rest I've seen to some extent, with the notable exception of Richards who for some reason I can't recall or find evidence of to that extent, but he appears on lists and I have managed to find some spectacular efforts at 3rd, but yeah.
With regards to Javed, he never stood out in videos, featured in literature and the stats never demanded a closer look. Guys the the subcontinent also tend not to get featured to that extent, if for nothing else, for the lowness of the Pakistani pitches, heavy emphasis on spin for most of India's and SL's history etc. but the great ones still stand out... Azhar, Dravid, VVS, Sunny, Younis and Jayawardene. Yes there are a couple more contemporary options, but those guys stand out.
It is harder than with batting and bowling, and as with them, it still requires a closer look. A mixture of stats, journalistic references and ratings, and eye test. Stats probably factors in least here, but is telling. For as many catches that, let's say Root had, he's never featured on a list or even garnered mention. And that's fair, warranted and validates what we've seen. Also validates the system to some extent.
And as I've said in the past, yes you look for consistency and safe hands, but also the difficult ones, the half chances, those leaning forward low ones, less the diving ones, those are stick or not, but yeah, that too factors in. Cathing with hands and not body, the high fast ones and ability to transition from pace to spin. Yes I also favor 2nd over first, those are where the more difficult ones tend to go and they also cover for first with the low ones that wouldn't carry. That's where the best ones tend to stand. Might be a personal bias, but that's where I stand.
Sorry for the ridiculously long ramble, hope it made some sense.