Roy worked his way up through the company to get an excellent job.

Poorer people cwould be better off if only if they worked harder.

I think the best way to write this would be “poor people would be better off if they just worked harder”

Theriggered by little things, dramatic change is now under way which is triggered by little things.

A more natural way to write this

It's a paradox that it is sunny while at the same time, it is raining.

Roy worked his way up throughby having excellent job.work ethics.

Or you could say "Roy worked his way up by doing an excellent job."

Poorer people cwould be better off only if they worked harder.

TheA dramatic change is under way which iwas triggered by little things.

It is somewhat childlike to use words such as "little" or "big", especially when you are an advanced writer. Try to substitute "little" with "inconsequential", "insignificant", "minor", "trivial", etc.