All my glass filters I bought used. They are so cheap locally that for me it makes sense to have same filter in several sizes in storage for apt fit than to down-adapt one large filter sample to the camera threads as needed.
Of course this is a great way to pile up stuff...
As alternative I also have packed in a bag a set of most used ones in the small Cokin form added with adapters, ready to take.
At that price point I see your point, however, if like some other photographers, you look for and buy, even used, "higher grade" filters, like B&W, etc, and have a range of threaded and Series filters/lenses from 28mm on up, especially those odds and ends you might pick-up or be gifted on the way, and want to multiply your ability to use more than one lens size for a single filter, then having a pile of various filter rings on hand, including sizes you might never use, cam be very useful and can be had, inexpensively
Personally, This last year or so, my focus has been on 67, 72mm and Bay 60/70 filters and adapters, for medium format lenses, and quality adapters for smaller lenses, to get maximum performance, for my dollars.
I am usually have to wait for the right deal to come alone,new or used, but I will wait until I have the money set aside, for a particular filter, one in the range I spoke of and hopefully with a good brass construction.
I'm able to do this, in large part, because I do have 75mm Wratten gels for all but the deepest ND, red, and inflated filters, plus a few of the extremes; most of my 50mm Wratten gels are colour correction but I will still keep looking out for b&w correction filters in that range as well, which will make step filters for ALL my non Medium format and small format lenses less critical.
I would like to be able to buy some good Brass step rings, but the expense is high, relatively speaking, even for good used ones, so this is on my list, should there be a second Stimulus, in the near future, and I'll use aluminum until I can replace them, one by one.
Good filters are best practices for your quality lenses, and how they are coated and made can make the difference in a non-issue photo-shoot/shot, especially in weather, trips on/by water, etc, and an unpleasant discovery, with no viable alternatives.
By-the-way, I do have a few Cokin holders and filters, mostly for 35mm lenses, which I do carry in my Big Bag of Filters, on car outings, but I do prefer good gel or glass filters, simply because that's what I started out with, so long ago, and so, they are a last reach option, in most cases.
Good Photographers can make good images with whatever they have, and I've had my share of "cheap" filters, but having good quality is never a thing to regret.
IMO.