PROFIT is not the only economic factor.
Let's say I'm in the business of selling normal goods (say, backpacks). Now, instead of just people going to my website or looking at crowdsourced backpack reviews, there's some cartel that has figured out how to dominate search engines and other sources so that almost all the customers see their middle-man stuff and buy through them instead of directly (even more extreme, maybe they spend massively on lobbying to achieve real rent-seeking via outlawing direct purchases by consumers, although that's not necessary for my argument).
These middle-men charge much higher prices than we'd see if everyone bought directly. But dominating the search-engines while the algorithms constantly change is ENORMOUS work, so these cartel companies pay almost all their revenue to a huge number of employees who work constantly to update their systems and maintain their middle-man dominance. You could say they "barely make a profit!"
So, in that scenario above, it's painfully obvious that the system is horribly wasteful and all-around negative for the economy aside from all the bullshit work of the cartel employees directly providing them income. The room for efficiency improvements are, in this case, nearly the entire REVENUE of the middle-men, minus only the costs of the goods themselves, not just their profits!!
Insurance companies do TONS of bullshit economic waste that is both necessary to the system as it is today yet unnecessary in a single-payer system. All of that waste is NOT profit but IS available margin for efficiency improvements.
But really, insurers are just one aspect. There's also total craziness in the core pricing that providers set and lots of other complete insanity in the status quo.
P.S. the middle-man issues described above are potential market-failures for any market system and just one of many reasons that dogmatic "free market" ideology is bullshit. That said, there's cases where actions to fix market failures only make things worse. Recognizing that free-market dogma is bullshit does NOT mean the opposing dogma is correct.