In either case, it's also like cutting off your left arm because you still have your right arm.
My experience is across three different companies now, and in the first two (not my current employer who... still do it wrong but it's the best I've seen), they fired the Ops guys and expected the Systems Engineers\Software Engineers to take those roles.
No overtime pay in either company for the extra work load that was placed on them (e.g. me) of course. So the only cost the companies incurred was productivity and the quality of work. The burden was entirely carried by the staff and to a greater degree the clients who accept a shoddier product and service.
Fortunately I quit both jobs to get to where I am now, though the old timers no doubt are still working ridiculous hours and are too scared to ask them selves "can I find better else where?".
Long term, doctors aren’t nurses and patients suffer. Eventually someone dies.
This ignores that it discards specialisation, not merely quantity, and that testers are generally cheaper than developers.