The technical defects of the 1943 models of the Panther had little impact upon it's ability to be mass produced, as it was a design made for mass production.
The initial production was throttled to fix the deficits before it was put back on full production. The first 3 months of production were severely defective, so they had to be fixed and production problems solved before production could ramp up, a problem the Ju88 had in 1939 when first put into production. For several months it initially had defects in production and with the design itself that needed to be worked out before mass production could resume. Though the design itself was designed for mass production it took time to iron out issues, which weren't even done by July as two burned up just exiting the train around Kursk.
The Panzer IV was not. That just under 2,000 Panther's were made in 1943 is actually pretty good for the first year of production for a brand new model of tank, roughly comparable to the T-34s. By comparison, the Panzer IV began production in 1936 but didn't come close to a annual production rate of even a thousand units until 1942... a full six years later.
Sure, the Pz IV was not initially designed for mass production, but it became more mass produceable with time (same with Ju88) as redesigns and changes were factored in to make it easier to make and more effective in combat. The 1942-43 model had greatly evolved since 1936. Yes the Panther's first year wasn't bad all things considered, a testament to the design for production ease, but also the huge expansion of AFV production resources and what could be done in war time. IIRC the T-34 got it's first 12 months in peacetime, so production conditions were quite different. The Panzer IV was not selected as more than a secondary support design until 1942 when it was realized that the 75mm cannon was a necessity, the Pz III couldn't take the 75mm gun, and a new design was not going to be able to replace the Pz IV any time soon. That was fully a matter of production choices, not the inability of the Pz IV to be mass produced.
It is if you use the resources that were historically used to build the Panther facilities to instead simply expand the Panzer IV facilities, like your proposing here. If you then recommend, then the result is the utter cessation of Panzer IV production in 1944 compared to OTL in exchange for a greatly reduced Panther production compared to OTL. Retooling assembly lines for a whole new design is a pretty substantial effort and causes considerable loss of productivity in the interim, as the Soviets found out when switching the factories that had been making the T-26 and BT-series to the T-34.
I'm not simply suggesting to expand the facilities themselves (except for subcomponents that could benefit from scales of economy), but phasing them in at any new facilities opened up (converted facilities at MAN for instance), which could get advice from existing production facilities, rather than having to figure it out on their own for a much heavier design that no one has experience with. Why is 1944 cessation of Pz IV production given, OP didn't suggest that at all.