It would appear they didn't feel they had enough after Crosby left, because they added Whoopi Goldberg in a small role.
Whoopi was added because she asked
to be on the show and at the time the producers thought the name recognition would help the series ratings. Her character actually stole a lot of Troi's development and in doing so weakened a main character. Not the best decision in the end.
Good point, but meh.... What were they really doing with that character though? They certainly weren't going to pull off getting the kind of relationship that Picard & Guinan had, by building up Troi. She was a subordinate, & not a very formidable presence, least of all enough to influence Picard in the way Guinan did. Bad mistakes in Troi's development right off the bat, really, & it never really improved much, but for a few exceptions
Personally, I think they could have benefitted more by optng for the Guinan type character from the get go, instead of clinging to the Phase II Decker/Ilia thing that Riker & Troi were spawned from