Sappers honestly aren't bad as there is 1-2 at most in a mob and likely just one. If you can deal with it, you can eliminate then attacking you at all. Far worse are Freakshow, Carnies, or others which drain over time and are bosses. I don't use FA on the build, but my BA/stone runs 10 toggles with 4 PS: +End, and unless I am facing something which does legit end drain, I pretty much don't even need to look at my end bar. Data below.
Recovery: 3.2/s
End Drain: 2.3/s
EndRdx: 14.2%
Recharge: 172.5%
I have the FF: +Recharge proc as well so I can cycle three AoEs.
My first go around with Rad during the low level was to slot Theft of Essence: +End in Radiation Therapy and that was outright swimming in end.