Please do not try to apply UK Rules and Practices to US Rules and Practices......they are quite different from one another.
As an analogy....swap London Area for Los Angeles area and throw in some mountains and high ground to boot......then apply what you just said for flights in that kind of congested area.....using UK Rules.
I seem to recall an Agusta 109 cutting down a Crane Boom in downtown London in bad weather conditions somewhat similar to the Bryant Crash.
I started a Thread about two weeks ago raising the issue of Low Altitude IFR Routes for Helicopters.....and it drew scant comment or discussion.
That is symbolic of the interest shown by the FAA and the American Helicopter Industry.
The Island Express operation that was involved in the Bryant Crash could be the Poster Child for the standard on-shore Helicopter operation.
Helicopter EMS Operators are the leading edge in IFR Onshore Operations these days as they are scattered all through the Country while the Corporate Operators were usually in the Big City Northeast or Chicago area.
The Gulf of Mexico Offshore Operators also do a fair bit of IFR flying these days.
Had there been a Low Level IFR Route system in place in the LAX area....and Island Express had embraced IFR Operations....perhaps that tragedy might have been avoided.