No, what you’re failing to grasp is that this trade doesn’t help the Islanders one bit except for you convincing yourself that the Islanders cap issues are currently on Varlamov. Take a look at their current cap situation. Almost all of the expiring contracts are guys that will not return, not long term issues.
As for the goalies themselves. Koskinen can’t stop a puck and the fact that he’s a UFA come July is Edmontons problem and no one else. Lou wouldn’t take him on (with Varlamov under contract for another year) unless the 3rd round pick was better, there was a useful prospect attached or the return is of the Islanders needs at the given moment (top 4 LHD or proven 30+ goal scorer). The latter part won’t happen with Koskinen involved however. This trade is going one step forward to go 3 steps backwards for the Islanders.