>Innovation requires reliable funding,
The way I see this argument is "Innovation requires an institution devoted to innovation, which requires reliable funding such as monopolistic or taxpayer"
As you say, on the 1-5 year horizon that's not true. Most successful startups are innovative, we need to look no further than Google itself with its pagerank innovation dominating search. Most universities have innovative researchers, and indeed explicitly set up innovative centers called "incubators" - but of course this is an example of government funding.
One of the first questions is what innovation requires 1-5 years. What about aha moment! innovation? Pagerank is an "aha moment" idea that takes a few months to demonstrate. There are more aha moment innovations than "grind for more than 5 years" I feel. Most of the "grind for 5+ years" innovations have yet to pay off e.g. fusion, super batteries, room temperature semiconductors.
A monopoly offers stable funding for some institution, but at what cost? No capitalistic incentive to improve product? Excess pricing because the consumer has no choice? Surely there are more fair ways to structure this.
Government control would destroy tech, government is not made for it. Look at Amtrak. A nationalized google would wither and get eaten alive by.. ... innovative search startups (themselves without research institutes funded by monopolies), or startups in one of the dozens of fields where Google has spread its tendrils.
Microsoft in its prime is a great example of monopolistic problems. They were a OS monopoly and kept leveraging that to smack down competition wherever they wanted to expand into. Google almost didn't make chrome - the CEO at the time was frightened that Microsoft would annihilate google if google should make a new browser. The monopoly engine allows for ease of dominating more and more industries through lateral growth. This all-encompassing destruction of captalistic price minimization, alone, is why we need to break down big tech monopolies such as google. An example of a "good citizen" non monopolistic company in this setting is Netflix - there's huge competition in entertainment field, they have innovated streaming tech, their profits are meritorious, and they haven't suffocated other fields like other big tech i.e. there's no Netflix phone, no Netflix video game console, no Netflix social media.
The other health of the Netflix / media ecosystem is it's not a duopoly. There's Netflix, there's Apple TV (hello, suffocating new industries!), there's Disney, there's paramount, there's hulu, and so on. This is what competition should look like. This is classic innovation in the capitalist sector, through brutal competition. We not only need to bust up monopolies but to consider duopolies or more generally - busting up groups of companies that collude to price or feature fix as holders of the majority of the market, which is what many duopolies are.