The r&d isn't expensive because these are legacy/old type chips. There isn't much r&d happening. They're made using old processes.
Any r&d is likely using different materials. Military stuff often uses different materials for specific applications.
The profits come from raising yields, which is much easier on older nodes.
Given the low transistor count, you could probably achieve speeds in the multi-10s of GHz, it would be so small.
A multi-core 99/4A would be hilarious to witness.
https://www.texastribune.org/2025/03/12/texas-congress-corny...
Similarly hyping up total R&D spending without a tight timeframe is meaningless, they will eventually spend X$ assuming the company survives indefinitely.
More charitably there’s meaningful differences between nodes, but it’s likely a significant portion of the workforce will be rehires.