I think the OP (and much of the subsequent discussion) is conflating two different things.
Do Klingon ship designs not change much? That much is apparent (DSC aside).
But does that tell us anything about Klingon technology? No, not really. The major powers in and around Federation space all seem to keep their tech at rough parity. (And given the existence of espionage, that's no surprise. Heck, we even have canonical evidence for this, in "Enterprise Incident.")
For that matter, how much does Federation tech actually advance between the 23rd and 24th centuries? The Federation obviously likes to have new ship designs, yes, and makes them larger and larger over time. But how much does the tech really change? Warp drives get faster; communicators and tricorders get smaller; and replicator tech gets more advanced (compared to TOS-era food synthesizers and recyclers) and integrated with holograms. But what actual innovations are there? TNG-era Federation tech seems fundamentally similar to TOS-era Federation tech, just somewhat more refined and optimized.
Do Klingon ship designs not change much? That much is apparent (DSC aside).
But does that tell us anything about Klingon technology? No, not really. The major powers in and around Federation space all seem to keep their tech at rough parity. (And given the existence of espionage, that's no surprise. Heck, we even have canonical evidence for this, in "Enterprise Incident.")
For that matter, how much does Federation tech actually advance between the 23rd and 24th centuries? The Federation obviously likes to have new ship designs, yes, and makes them larger and larger over time. But how much does the tech really change? Warp drives get faster; communicators and tricorders get smaller; and replicator tech gets more advanced (compared to TOS-era food synthesizers and recyclers) and integrated with holograms. But what actual innovations are there? TNG-era Federation tech seems fundamentally similar to TOS-era Federation tech, just somewhat more refined and optimized.
