Check the Guide under "Leaden Salute" sets. DP > Moly > Doomsday is what the gear progression tiers show.
I also use Fomal, and I think I AMAN voucher'd my Moly cuz I was lazy and only wanted to keep one gun for shooting ws.
The gear progression shows difficulty in terms of obtaining them, not 2nd best alternative to DP. It assumes Fomalhaut is out of reach for those still gearing up thus not in there.
I am assuming actual hierarchy would be DP > Fomal > Moly/Doomsday/Arma > Everything else?
This is correct, with the exception of warcry+crystal blessing active. If both are active then moly may beat Fomalhaut if your ws set has lowish mab. If you are in a situation that you over TP a lot due to waiting for SC then moly wins too.
The point that favor moly depends on mab in gears
Spreadsheet shows using a low tier leaden set(only 20 mab on herculean, no relic +3 body)
At 750-800 over tp or tp bonus buffs moly wins. But that's not the case with relic +3 body and 40 mab Augmented herc.
Also it's not totally impossible to ws at 2000+ in blm sc situations. With tripe shot up and shooting in between sch sc getting 3000 tp ever leaden is totally doable.
Edit: just recheck numbers using different sets, fixed wording.