If you want to further strengthen your characters to better prepare yourself for WL6, staying at WL5 for a little while is okay I think? The main draw of WL6 is guaranteed 5* artifacts from domains so If your party is ready to take on lv 90 domains I say go to WL6.
People advise against holding off on ascending at WL2 (AR 25) and WL4 (AR 35) because if you stay too long before ascending, you can actually skip two world levels and make things more difficult for yourself.
This isn't an issue at AR 45 because if you do accumulate enough exp to make the jump to AR 50, there's another ascension quest there instead of automatically raising your world level.
The jump to WL7 however may or may not be worth it from what I hear due to the drops.
Claude von Riegans acquired: 2/2 (academy, brave)
Ephraims acquired: 4/5 (legendary, brave, duo, winter)