How important is tank gear as WL

Hey there :)

after only playing Tbc and wotlk back in the days, i started playing a WL in Classic fresh.

My gear is now ready for AQ40 so i started reading some guides.

What i didnt know is, that for tanking the Twins u need a complete Shadow Resistance gear set.

Do people expect warlocks to have that gear? I will start getting it, but it will take me quite some time and i would really Like to start with AQ40…

Thanks in Advance :)