I reckon this devolution problem is pretty easy to fix...

First off - a basic premise: any powers devolved to any UK member nation's parliament or assembly is automatically devolved to the others.

Secondly:

• the Westminster parliament splits its time into UK, England, England + Wales, and England+Wales+Northern Ireland matters.
• only MP's elected for constituencies within the appropriate country can vote in those matters.
• as matters devolve the UK-only debates will become shorter and fewer; as a consequence the number of MP's needed to discuss is reduced by increasing (and balancing) constituency sizes.
• Once UK legislation only needs a small amount of time each week at Westminster then a major exercise of reconsidering the number of MP's elected to the Commons can be started, potentially replacing the English "subset parliament" with a fully elected English Parliament; and the House Of Commons with a different structure.

So, no need to increase the layers of government or staffing.

No need for expenses to increase (in fact they should start diminishing as overall Westminster time decreases).

No democratic deficit.

No West Lothian problem.

Of course, it doesn't address the issues of trustworthiness et al...