The general concepts of those things sure, but the specific applications of them more questionably.
Bet lets say we assume all these things are wrong. It still does not touch on dialectical and historical materialism, which is what marx formed his views from. You could argue dialectical materialism does not belong to marx as it was independently created on multiple occasions, but historical materialism as a working theory of history certainly does, and any specific historical materialist analysis of any point in time is dependent on known information about that period of time, and so conclusions can be false by using bad information, for example.
Likewise, the very nature of the assumptions behind historical materialism, that society is shaped by its conditions, will necessarily change as those conditions change. The stance of some modern historical materialists for example are that marxs economic ideas described things and were valid interpretations in his time but no longer describe things in our time. (notably the dprk, who presupposes historical materialism as valid, but no longer considers itself marxist despite marx in his capacity of dialectical and historical materialism still being foundational to their worldview- so i suppose they agree with your definition of what marxism is)
This becomes a problem of semantics ultimately however, as marx and engels contributed three main and distinct thing to the left: dialectical materialism (or at least its most refined form), historical materialism which is a dialectical materialist theory of history, and marxs study of capitalism which is a historical materialist analysis of capitalism.
Thus if one were to argue against dialectical materialism, they would be arguing against all three. If they were arguing against historical materialism, they would be arguing against two of the three, and if they were to be arguing against marxian economics they would be arguing against only one of the three.
There are moreover people who consider themselves marxian economists who have added entirely new ideas to it or disagree with marx in some ways. What do we call these people? Is marxism to be taken as an economic school? a lineage? some combination of the previous three things?
If we call it a dogmatic adherence to the specific and exact economics marx described the first person to argue against it would be marx himself!