I honestly thought Crosby was one of the weaker actors of that season 1 main cast. Very daytime soap, which it's true, that such could be said of a number of them at that time, but it worked the worst for her imho, which explains her discontent, & their willingness to be done with her quickly.
Why would they make Geordie the chief engineer if they had a regular character with no job? Worf would have been the obvious choice for that had Tasha stayed, he did as much engineering in season 1 as Geordie.
Because there was always going to be the intention of making Wesley an acting ensign on the bridge. So Geordi was a place holder in the helm position, & I recall Geordi being WAY more relevant in techno use in season 1 than Worf was. It was a no-brainer easy fit for him to go below deck imho
Frankly, Geordi & Worf had way better potential for development than Tasha (Albeit Geordi withered on the vine a bit) There just wasn't room enough in the bridge dynamic for all of them to bloom regularly. They were looking to ditch somebody, & a number of heads were on the block. I think they chose wisely, because eventually they did FAR better with Tasha 2.0 in Ro Laren, who could instead be a part-time feature like Barclay.
The very character nature of Worf kind of impedes on a security chief character like Tasha eventually anyhow, were they to coexist. It's why Worf had to become XO on DS9, because he & Odo couldn't both occupy Odo's security chief space. Worf & Tasha are at odds imho. Having a tactical military officer type AND an engineer (who acts like a belligerent Klingon) both in the briefing room together is redundant on TNG. There was more latitude for it with Worf, Kira & Odo in wartime DS9, but not on utopian 1701-D.
Crosby never sold me as being the "Tough" archetype that Forbes eventually did better anyhow. She was the one that was most miscast imho. I'd have preferred if she'd been dropped on the bridge in season 1 in a blue science suit, with TWO at the forward-facing back console, her
alongside Worf as tac/security chief. THEN I could see keeping everybody. Heck, I even kind of wish Dr. Selar had kept returning as a part-time feature after season 2. We could've used some more Barclay, Ro, O'Brien types aboard, which is why I think everyone loves the Lower Decks episode so much.