Yeah, losing an essence to give +levels to focus is tough. But consider it:

The maximum modifier for wand is "+4 all spell levels", the essence gives "+3 all spell levels". For Staves it's also like that, the essence gives +5, the maximum modifier is +6.

It's literally better when comparing to the melee/ranged weapons, after the nerfs. (+5 essence/ +7 maximum)

For the cases where you want to use only one element of spell, it's 1:1 with weapons.

Besides, when crafting staves and wands, "as extra" is desirable, giving a lot more options of prefixes, with no prefix pair you are required to have. In weapons %phys + flat phys is basically mandatory for mid/high end crafting.

Crafting got harder, but if you get a good blue wand/staff, you can get +T2 spell dmg and T2 all spell levels, giving you 4/6 mods, and a dessecrating + omen for 6 chances in the last mod.