That is probably the easier way for SE to accomplish "balance" sooner, but if the weapons were designed for Delve's, the mobs in Delves will have to be adjusted too so they are beatable with current weapons, as it seems they were designed for them, so it's just a re-balance of 1 event vs many events.
This probably would have popped up, had Delves been on the test servers for us to try out before actual implementation.