Another basic problem with all these alien races. The Klingon Empire is all Klingon. The Romulan Empire is all Romulan. The Cardassian Empire is all Cardassian.
There are a few exceptions. The Klingons held the Kriosian system, but you never see Kriosians working on Klingon ships. We never see Remans (screw Nemesis).
Contrast that to the Federation, which is a combination of dozens of alien races. It's not humans vs. Klingons, or humans vs Romulans. It's Humans/Vulcans/Bolians/Andorians/Tellarites/Trills/Betazoids/numerous others vs. Romulans. How could any other empire compete? There would have been 100 times more Klingon individuals than humans to be equivalent.
The closest thing we see to an adversary with diverse members were the Sona in Insurrection. They were different species working together. Then there's the Dominion, though they bred the Jem'Hadar and Vorta. The Dominion bringing in the Cardassians and the Breen was never going to last.