The Romulans still need to be considered a viable threat in the TOS era. Having them restricted to a very small area of space with sub-light drives is really a non-threat to the Federation, or even any Federation allies if it would take a decade or more to get to the nearest non-Romulan system.
Having lower powered FTL drives is fine. Even if they are only up to Enterprise era warp factors, they could at least be a threat to the surrounding area.
Having lower powered FTL drives is fine. Even if they are only up to Enterprise era warp factors, they could at least be a threat to the surrounding area.