Marx isn’t praising productivity, especially not in the manufacture-division-of-labour.

Sections two and three describe manufacture, and sections four and five are harshly critical or condemnatory of it both in itself and as it exists under capitalism. This critique begins in section three, towards the end, when Marx talks about unskilled labour and the separation of activities which are rich in content from those which are tedious.

Section four has quotes like e.g.

This is not the place, however, for us to show how division of labour seizes upon, not only the economic, but every other sphere of society, and everywhere lays the foundation for that specialization, that development in a man of one single faculty at the expense of all others, which already caused Adam Ferguson, the master of Adam Smith, to exclaim: ‘We make a nation of Helots, and have no free citizens’.

Where Marx 1. quotes a bougie economist for extra authority on the division of labour sucking and 2. says that this (i.e. Capital) is not the place to discuss this in general. (For such discussion, see e.g. Contribution to the Critique of Hegel’s Philosophy of Law).

Section 5 is even more openly condemnatory e.g.

[Manufacture] converts the worker into a crippled monstrousity by furthering his particular skill in a forcing-house, through the suppression of a whole world of productive drives and inclinations, just as in the states of La Plata they butcher a whole beast for the sake of his hide or his tallow

P486-88 (Penguin Fowkes translation) also shows how, while the political economists view the social division of labour “as a means of producing more commodities with a given quanitity of labour, and consequently of cheapening commodities and accelerating the accumulation of capital”. He contrasts this view with that of the few modern economists who don’t fetishise exchange value, profit, etc, (as well as the ancients) where 1. division of labour allows people to do stuff they like and are good at and 2. without at least some division of labour nothing can be done.

I said above “Marx has praised the division of labour as increasing productivity (especially in Ch.14 Section 2).”

You also said:

This is an important passage for understanding what Marxism would look like. Here Marx talks about the planned economy.

Capitalists do accept the ‘planned economy’, so long as it’s within the walls of a factory. … So Marx wants to bring that increased productivity to the economy as a whole by bringing the same sort of rational planning into the economy as there is in the factory.

Which is the part i disagreed with