Aside from arriving in the fourth seasons of their respective shows, there's no similarity.
From a writing perspective, Seven and Worf serve an almost identical function, each to their respective shows. Seven didn't overshadow Voyager, but she received more prominence over certain other characters, like Kim, Chakotay, etc. She definitely didn't get more focus than Janeway, or the Doctor. Worf was likewise given more prominence over O'brien and Bashir, and probably Dax initially.
The both began their season's with a two-parter:
-Worf, an intermediary to a third party in a Klingon War.
-Seven, an intermediary to a 3rd party in a Borg War.
They both had about 4 or 5 character focus episodes in their respective introduction seasons.
They are both characters caught in the middle between two worlds, and can't fully embrace one or the other.
They both wear distinctive uniforms that cause them to stand out/be separate from amongst their peers.
Worf is the only Klingon in SF. He wears a huge silver sash. Seven is the only Borg, she wears her own uniform and has biomechanical implants all over her body.
There are many more similarities, but that's the idea. Seven and Worf were a big opportunity for new stories where(some) existing characters may have become strained, or increasingly difficult to write for. Seven and Worf probably also added a nice boost to ratings.
