One thing often overlooked and a reason why newsstand distribution ceased is that the retailers didn't really want to carry comics, their price point was too low to pay for the space they took up inmost cases, and it was a reason why DC experimented with formats so much in the 70s (60 cent giants, $1 comics, etc.) in an effort to find a format that appealed to dealers and would get better placement on the stands. Far too often, the comics would arrive in bundles at the newsstands/dealers and maybe one or two would be open and put out, but the rest remained bundled and then were returned for credit without ever getting put out to be sold. Sell through rates were falling terribly (i.e. the number sold vs. the number printed) on newsstands throughout the 70s and 80s, which made the guaranteed sales of direct distribution more appealing. The direct market was meant to sell comics to people who already knew what they wanted though, hence the non-returnability not being a factor for early direct retailers. The newsstands were still the growth market where new readers could discover comics, and it was that symbiosis that lead to a bit of recovery in the later 80s and early 90s-kids were still discovering comics in all the old places and then finding/going to comic shops once they were already fans/readers. However, the easy money of the direct market was fool's gold, and once the newsstands disappeared, the direct market was left selling to an already existing customer base without much chance for an influx of new readers, one that would shrink by attrition without replacing those who left. The direct market was never designed to fond or appeal to new readers and non-returnability works against retailers being able to stock books on the shelves on the chance a new reader comes in, discovers and buys it, hence we have the stagnant shrunken market which exists today where only 2-3 titles a month sell anywhere close to what X-Men was selling in the early 70s when it was a bi-monthly reprint book that got cancelled for low sales. So newsstands left comics just as much as comics left newsstands, and there was going to be a market shift/correction of some sort because newsstand distribution was going away regardless of what the publishers chose to do. So yes, losing newsstands was a big blow to accessibility, but it was going to happen whether comic publishers chose to abandon it or not. It was already a sinking ship. The problem was no one developed an alternative to newsstands that allowed for discovery by new customers and the industry doubled down on the reliability of guaranteed sales to accounts who bought on a non-returnable basis. And when entropy caught up with that decision, there was nothing in place to offer replacement readers or growth.
There is a growth market in comics now-but its comics in book form sold in the YA market of the book trade, not in monthly periodicals sold anywhere, as periodicals are an antiquated product type that is a dinosaur in the current marketplace. The history of comics is one of changing formats to fit the marketplace, from the big anthologies of the Golden Age onwards, but somewhere along the line, the format of comics got ossified an it no longer changes to adapt to a changing marketplace. If you look at when and where there were major shifts in sales, there is usually a change in format that helps fuel a recovery (though each recovery never reaches the heights of what came before, it does bounce back some), whether it is in size, price, page count, or what have you. The market has continued to change and evolve, but the comic format has not. It ossified sometime in the 80s with only price changing as cost of production spiraled.
I don't think you will find a lot of actual numbers for ealry sales, as many of the publishers had ties to somewhat shady operations with criminal activities and a lot of money was skimmed from comic sales and channeled there, so actual revenue/sales info was kept pretty close to the vest. There was all kinds of chicanery with titles switching, numbering changes, sudden cancellations, etc. to obscure what was actually selling or not selling and how much revenue was being generated. It wasn't until the 60s and postal requirements for statements of ownership that any actual hard numbers were released into public knowledge. so I am not sure the OP is going to be able to get any clear answers to his question.
-M