You might be right, but keep in mind that flash has been scaling due to the shrinking semiconductor feature sizes (and additional layers/etc). So a large part of flash's core R&D & production costs are being spread over all the logic being produced. That has been hitting a wall, so while the capacity/price curves for flash look nice, they likely won't continue, which leaves open the possibility that if rust actually gets a 4-5x boost in the near future the current market trends will continue. SSDs for perf/power/size and mechanical harddrives for bulk nearline storage, leaving tape where its been for the past 30 years, as an archival technology.
Horizontal feature sizes for flash memory stopped shrinking years ago. The continued improvements in density and production cost have been the result of R&D that is very specifically focused on 3D NAND flash memory and has little in common with R&D for logic circuit fabrication.
That said, on the horizon of multiple years, I agree that the future scalability of NAND flash doesn't look quite as promising as HAMR/MAMR for hard drives. How that translates into actual product demand and adoption will probably depend on the relatively unexplored question of how much performance per TB our applications actually need. 40+ TB hard drives might not be fast enough to actually serve as nearline storage for that volume of data without eg. multi-actuator technology that essentially gives you more than one hard drive sharing a common spindle motor. Meanwhile, there's no question that QLC NAND flash definitely has adequate read latency and throughput.
Multi-actuator tech sounds interesting, and I wouldn't be surprised to see drives with 5, 10, 50 or 100 read heads per platter at some point.
With 100 read heads per platter, typical seek time is cut by a factor of 100. That won't let them overtake SSD's, but at least allow them to close the gap.
So far, nobody has announced plans to manufacture hard drives with two read heads per platter, so speculating about 100 heads per platter seems rather unrealistic. The multi-actuator technology that is actually being developed by Seagate still has only one read head per platter, but out of the eight or so platters in a drive, the read heads for four of them will be controlled by one actuator and the read heads for the other four platters will be controlled by the second actuator.
Going all the way to 100 read heads per platter would be insanely expensive and would massively increase drive failure rates, while still leaving them about four times slower for random reads than the slowest $35 SSD on the market. This will never turn into a viable product.
