You really do seem to have underused magic to a spectacular degree in what is a long game against the AI.
Put it like this, using site-searching spells, you
should have completely found all earth, death, and fire sites in your realm courtesy of Svartalfs (1 in 4 has 1 fire and with FD you can make the cheap fire path booster...), and all air sites using Vanjarls. The Hangadrotts can also be used to find holy sites up to 3 by manual search.
...and you SHOULD be using site-searching spells. They pay off handsomely in the long run and, against the AI on a larger map, you are playing a long game. If you consider Helheim "nearly magicless" you are doing something dreadfully wrong.
With a bit of spectre summoning using your big death gem income, you'll end up with some spectres with W (which is enough to make a water bracelet) and some with S (which needs a 20 gem empowering to start making pathboosters - a one-time expense), so even if you don't use your pretender for early searching and even if you don't hire the caster mercenaries (or they don't show up) you should get all water sites searched as well.
That's FAWEDH covered, completely and fairly cheaply, using just national troops and death summons, you only lack access to natural and blood (actually, you have access to blood, but it isn't worth it for Helheim). If you don't want to use death summons, astral will have to rely on independents and water on your pretender casting voice of apsu each round - which he should be doing. If you go this way, your death gems should (as soon as you've made your first dwarven hammer) be spent on creating skulls for research. That does wonders for the research graph. Either way, you'll want some skulls to get research to be tolerable, and that means beelining for construction 4 early on.
That's way more magical access than most nations have, and you should exploit it.
With the national magic available to you (with constructed pathboosters or bootstrapping through the elemental royalty and then using them with pathboosters) and your F9W9 pretender, you have access to...
Global enchants like: Well of Misery, Eternal Pyre, Maelstrom, Dark Skies, Gale Gate,... and more.
Summons such as: All elemental Royals, Legion of Wights, Trolls and Sea Trolls, Catoplepas (AOE death attack... you can use squads of these as very heavy artillery), and more, and more...
[And that's not counting kitting out some of the better commander summons as thugs to really help your armies put the boot in or kitting your Hangadrott's out as Soul Vortex thugs or alternatively using them as Shadow Blast devastators]
And, of course, if even that isn't enough to break the stalemate, then you can just start killing his population using bane venom charm carrying scouts and casting deadly rituals at his civilians instead. See how how long the AI can continue to afford and recruit monster armies when you kill its source of income.
With EA Helheim in any longer game you have easy access to a high gem income and most of the magic in the game, even if you have chosen income-minimizing scales - use it!
Short game vs humans would be something else, of course.
