Your problem is your weaving then, at nearly max reduction (cp) already you should be able to sustain for ~60 seconds (Which is all the fight should go on to begin with). I run a similar build often with 800 regen and the second I stop weaving is the second I start wondering why I have no magicka.
edit: PuG will be PuG, your build is designed around a healer having a clue and fights being a reasonable amount of time. The longer a fight goes on the harder you will find resource management, either account for inexperience (by switching to atro from thief for it) or talk with your healer for more return (ele drain/syphon etc) before the pve environment starts.