This season highlighted that one major problems for this show is that Bojack is running out of relationships to ruin.
Here's all the relationships Bojack has ruined:
S2: Colderoy, Wanda, Charlotte, Penny
S3: Todd, Oliver, Sarah Lynn, possibly Bradley
S4: his mother
Both Wanda and Gina aren't someone from Bojack's past and were introduced in the season Bojack ruined their relationship. As a result losing them isn't as impactful as Bojack can try again next season to get into a similar relationship.
Personally I found Gina and her relationship with Bojack less interesting than his relationship with Wanda. It may have been because Gina didn't have much of a personality, was mainly defined by her relationship with Bojack, and she only seemed to be in this relationship so that Bojack could ruin it at the end of the season.