2K sounds about right. To answer your question about the parse, Shields are two components - the heal and the shield which is based on your heal. Even though it's technically a 300+5% potency AoE heal for Aspected Helios, the parse is actually only counting 150+5% due to the nature of shields (use similar math for Aspected Benefic).

Diurnal gives you more overall HPS because HoTs are awesome potency for their GCD and efficient for their MP cost and you generally want to keep it up 100% of the time to maximize that benefit. For example, Aspected Benefic Diurnal is 1,030 potency in a single GCD (over 18 seconds). Nothing in the AST (or any healer kit aside from Regen) can really compare to that kind of efficiency in a single GCD.

Overall 5K total HPS w/ 30% overheal sounds right for the fight and I don't feel you have anything to worry about. I was in Sephi EX a few nights ago and I was Diurnal AST with 2.9K HPS while my SCH partner was 2.3K HPS just to put that into perspective. I've also been in a Sephi EX with a really good Diurnal AST who was basically doing 3.4-4K HPS and I was sitting down at around 700-1K HPS while rocking 650 DPS by the time Phase 1 was up and our numbers eventually shrank to something like 3K for them and about 1.5K for me without too much of a hitch in P3.

TLDR: YOU'RE FINE! =D