Is it okay to refer to a certain period of time in the past when we speak about a fact that is still true today?

Is it okay to refer to a certain period of time in the past when we speak about a fact that is still true today?

For example:

"This idea has for a long time been one of the central topics of debate in philosophy, especially from the early 19th to the mid-20th centuries."

How can I rewrite my sentence to say that although the idea is still a central topic of debate in philosophy, it was "more central" (and more discussed) from the early 19th to the mid-20th centuries?

Your sentence as written implies that the idea is still a central topic of debate today, but not the central topic it was from the early 19th to the mid-20th centuries. Given that this seems at least slightly contradictory, I would consider revising it as follows:

"This idea has for a long time been a topic of debate in philosophy, especially from the early 19th to the mid-20th centuries."

This revised sentence implies that the idea is still a topic of debate today but not does not command the same ("central") attention it had from the early 19th to the mid-20th centuries. If you want to maintain your emphasis on central, you could write:

"This idea was a central topic of debate in philosophy from the early 19th to the mid-20th centuries."

This does not imply that it wasn't a topic of debate earlier or later, only that it was not a central topic. In this second rewrite, for a long time is implicit in, and communicated precisely by, from the early 19th to the mid-20th centuries.