At diagnosis B cell function is reduced to 50% of normal. (below)
Further there is only a 50% chance of those beta cells being restored to their normal function after 10 years of diabetes.(above
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6399621/) Which you challenge apparently because you deny that the beta cells malfunction in T2.
The Pathologic Basis of Disease Progression
At the diagnosis of type 2 diabetes, β-cell function is typically reduced to 50% of normal [as shown] by HOMA modeling and to a greater extent on dynamic testing (
1,
18). Despite the initial effect of diet and oral therapy to lower glucose, observational studies have shown that disease progression is associated with inexorably declining β-cell function and progression to insulin commencement, with relatively minor changes in underlying insulin resistance. …...Postmortem pancreatic pathology studies, based on presence of staining for cells that contain insulin, have suggested that β-cell mass is significantly reduced in type 2 diabetes in comparison with age-, sex-, and BMI-matched control individuals without diabetes (
2). Although it is accepted that increased apoptosis plays a role in decreased β-cell mass over time, pancreatic pathology findings in a large cohort of European subjects indicate that apoptosis alone is insufficient to explain
the profound islet dysfunction in established type 2 diabetes (22). Other factors must contribute to the described
decrease in cells that stain positive for insulin in the pancreatic islets.
https://care.diabetesjournals.org/content/39/11/2080