Generally, a delamination of a QUALITY marine grade hose would be expected from abuse in the form of severe overheating (expecially dry runs that would also kill a engine or two) or mechanical abuse from a really agressive bending installation activity or damage.

Absent some sign, I wouldn't rush into that course of action either.

Delamination does happen, after you look at the exit from the elbow and see it looks "new", I'd look elsewhere.

On the issue of backpressure, I suspect that within tolerance levels (that's not into extremes), the issue would be first, some minor effective horsepower decrease with a decrease in fuel efficiency; and then, some overheating.

You can solve these issues by scaling back RPM's slightly.

Some the issues could have to do with the pitch you prop, etc.