I wouldn't necessarily call it a myth. I would, though, say any efforts to compare the quality or quality of teaching and learning in the past to that in the present always requires several caveats, warnings, and context-setting.

First, to your question about the "decline" of "inner city education." It's important to stress that the public's perception of what happened (and happens) in urban schools is usually skewed by media coverage and representation. I wrote a response to a question about the portrayal of urban schools as "war zones" in 80s movies here.

On the same note, in the period you're talking about, the difference between rural and urban education was profound and it's difficult to lump them together. By the end of the 1800s, most cities had had an established, funded (if not well-funded), and bureaucratic school system. This meant teachers were generally better trained and there was an infrastructure around books, supplies, and resources, and there were some degree of administrative structure, including grade levels. In contrast, rural teachers often had to deal with inconsistent student attendance from children of all ages and a lack of any kind of meaningful support while being only a few years older than her oldest students. Urban teachers were typically departmentalized outside the early grades and could develop expertise and specialized techniques for their content. Rural teachers were responsible for every subject and in many states, had little or no guidance regarding content specifics. What bureaucracy did exist around rural teaching was typically focused on bean counting and collecting general, non-pedagogical information about what teachers did. As an example, I could dip into the NYS archives and tell you want textbooks teachers in rural NYS in 1852 had on their shelves or desks but I can't tell you what they did with the textbooks. Meanwhile, before the 1850s or so and the rise of the bureaucracies, we don't have a great deal of primary evidence to work with regarding what happened in the classroom.

In other words, our understanding the fine grained, day-to-day details of how teachers in the past taught (basically before cameras in the classroom) is hazy. Larry Cuban, who literally wrote a book called "How Teachers Taught" undertook the Herculean task of trying to pull together enough evidence to make claims about pedagogical practices and described his work as facing the same bind as paleontologists who find a shard of a skull bone, which is a small part of the skeleton, much less the population of people they want to study. At the same time, much of the writing about what happened in classrooms comes from those we have to consider unreliable narrators for a bunch of reasons, but most notably because they weren't neutral observers - they were advocates for change.

A large quantity of words put down by those who described classrooms in the period you're asking about were put down by schoolmen, a moniker for school administrators, professors, and consultants who were constantly pushing for change. That change typically came in two flavors. The first was similar to what you raised in your last paragraph: schools need to go back. Back to when schools was better. You know, waves hand in a general direction towards the past back then. The second flavor was towards the future. In the time period you're asking about, the push towards the future can generally be described as student-centered instruction, a pedagogical approach advocated by those who saw themselves as part of the Progressive Education movement. In a nutshell, the biggest difference between teacher-centered and student-centered instruction is who is doing the talking. In the teacher-centered classroom, the teacher does most of the talking and is mostly commonly what we see in the modern classical model or even with lecture-based HS and college classrooms. Student-centered classrooms usually involve more talking and discussion from students. This isn't to say teachers never talk in student-centered classrooms or students' voices can't be heard in teacher-centered ones, it's more about what happens most consistently.

So, in effect, we can't "go back to a pervious period of time" because we don't know what was happening in classrooms during that period of time. We can speculate, but that's it. Meanwhile, at no point in American education did classrooms or learning experiences for all children look the same. It varied not only due to urban/rural as described above, but on class, race, location in the country, time, and a child's disability status.