I'm torn about Chloe's return. It just feels like Lana's return all over again (she has only two episodes left!)
To be blunt, the relationship between Clark and Chloe has diminished between the end of S8 and the course of S9. Everything bad that happened was blamed on Clark. Chloe never took any responsibilty for what happened at the end of S8 or what she did during S9. And yet she comes back and everyone is lying at her feet. Martha is even the mother Chloe never had even though that is a total retcon when you look at the early seasons.
Chloe, like Oliver is an "ends justifies the means" kind of person - something that Clark by definition is not. As a character trait in a fictional universe that is ok in itself. But Clark has to challenge that attitude. For heaven's sake, she now leads the Suicide Squad and nobody is bothered by it. He was even ok with putting the VRA guys into the virtual reality indefinitely.
And have you noticed that she changed her reason for leaving three times already? First it was because the helmet showed a danger to the JLA (which she conveniently did not warn them about even if it was vague). Then it was because she exchanged herself for Oliver. And now she did it because she needed to leave Clark so he can "grow". Last year she was mad at him because he worked alone in Checkmate - and again he got blamed for her going on a solo mission. A mission he knew nothing about, she proposed and Oliver let her go - but Clark was the one who had to apologize for - for what exactly?
I bet if Chloe should meet Darkseid that she would repel it because she's so "pure" (at least in the writers' minds).
There are only 8 episodes left (episode 21+22 being a two-hour finale) and they need to let Clark take the charge - like he did in Salvation.
What I also don't like about this season is that due to budget reasons it's always the guest stars who get the CGI time. Aquaman blew up the oil rig (Patriot). Hawkman saved Lois (Icarus). Chloe gets the Matrix fight (Collateral). When was the last time we actually saw Clark in action?
I liked Chloe. A lot. Especially in seasons 4-6 even though they had to dumb Clark down so she could be useful at all (just compare a first season and a fifth season episode and how Clark solves the case). But their friendship changed when she ran off with Davis and blamed the whole Doomsday debacle on Clark even half a season later (Conspiracy).
Maybe it would have been better if they had let her go at the end of S9. Maybe go on a soul-searching walkabout.