No, There is no imperative to create a new construct here.
When a metaphor ''loses its metaphorical properties'' due to the demise of colloquial meaning of its components, where the meaning remains we call this an idiom. Where the meaning is lost entirely, we call it a dead metaphor. Both of these descriptions are accurate, depending on the time, place and persons from and to which the phrase is spoken or written.
Also I believe the following phrasing manipulates the outcome of the discussion:
'high point [e.g., of a career]'
The above definition includes his very own implied assumption of "high" being strong or successful! It would be far more accurate to simply use the following phrasing in our definition of the zenith of a career:
'strongest or most successful point [e.g., of a career]'
I believe this is simply a discussion of the difference between metaphor and idiom.
In the case of the phrase "Falling in Love" we're really looking at an idiom. Whether or not a person understands this phrase is a combination of 1) whether they've heard that particular idiom, and 2) whether idiom exists in their native paradigm at all (e.g. certain languages have no idioms, and the concept of idiom can be a challenging new one).
However, this is completely separate from the fact that a limber mind can interpret meaning in places where it has not been literally defined. We call this metaphor.
Best Answer
a tough slog, or a long, tough slog or, to be more positive, a tough slog, but rewarding
slog, from The Free Dictionary means:
We see that a slog is by definition difficult and long. A tough slog adds emphasis to the difficulty and a long, tough slog adds emphasis to the prolonged nature of the slog.
Examples of tough slog and long, tough slog
From The Hill
From The Washington Post
Finally, I think you need to say that the experience was positive. Thus, my suggestion is a tough slog, but rewarding, or a tough slog, but worth it.