Will the hypothetical employer reject your application on the ground that you lack the relevant job experience for the position you're currently applying for?
You could have 30 years experience as the top lawyer in the country, but if you apply for a software engineering position, it won't be useful.
But that same lawyer could apply for a decent number of positions which are not "lawyers" but can use that experience (for example many politicians have legal backgrounds, for better or worse...).
The point is it is what your experiences are that matter. Being a legal assistant you do things X, Y and Z. Some of those things can translate outside the legal field, some cannot.
Experience doesn't have to map directly 1-1 to a potential job requirements. But the usefulness of it should loosely map to the needs of the potential job. The important thing is making clear how X, Y, and Z can be useful for the future job.