I agree up to a point, Q. Where I stop is your description of B'rels suiciding. Those are Jem'Hadar tactics, and I'm pretty sure the Klingons would find such tactics dishonourable.
Much is made of the Klingons' loss of Praxis. Losing one moon that was "their main energy production facility" does not stop a stellar empire every bit as big (or even bigger) than the UFP from having the resources to build battlecruisers. All you need for that is asteroids or planets to mine for resources and standard electronics-equivalent manufacturing capability.
If Praxis is their only or main dilithium mining project, then that would affect the number of ships they could power. A B'rel will use pretty much the same amount of dilithium as a K't'inga (based on the size of an Enterprise crystal as seen in 'The Alternative Factor' and the size of a B'rel crystal as seen in STIV), so I'd say if it is the number of ships that is limited, the Empire would build ships with far more capabilities than a B'rel. Battleships, instead of cruisers or fast patrol ships (PFs).
I'd just say that the cruisers of the Empire were off doing more important things. Putting down rebellions, conquering new planets, defending against active incursions by the Mirak, Hydrans, Sha'kurians, even Romulans (who thinks that Kang, Kor, or Koloth defeated the Roms at Klach D'kel Bracht from B'rels instead of K't'ingas?)
For patrolling the Fed border, where the Klinks know that the UFP is too spineless to attack them, they would assign squadrons of B'rels for patrol, supported by the occasional k't'inga if the situation got too heavy.