There can be some discussion about what weak means. None of the prayers (except possibly soulfire) are weak.
Like a 5+ ward save against shooting is strong
Ehh, I wouldn't say strong. The prayers are mediocre at best honestly.
I've seen several people consider them "undispellable spells" (that only work 58% of the time), and they are essentially a mixture of Enchantment- and Assailment-spells, so lets compare them as such:
1) Shield of Faith. A 5++ vs shooting (only).
Good against armies with alot of shooting, terrible against armies with no/little shooting.
Comparable spells are the 5++ from Lore of Battle, the 5++ and defended obstacle but cannot march/charge from Lore of Elementalism, the 6++ against non-magical + Fear from Lore of Necromancy and the 5++ until the end of your turn from High Magic.
Shield of Faith is basically a shooty-equivalent Shield of Saphery from High Magic. I'd rate it one of the lowest of the bunch, because ultimately, generally speaking, melee has a larger impact than shooting, and Shield of Saphery makes you dictate where the benefits are (you are the active part, you give it to a unit and charge in), while Shield of Faith is a reactive power, the opponent can simply shoot at something else.
2) Soulfire. D6 S3 AP2 Flaming Magical hits.
I mean yeah, this is just a bad Assailment spell. Not even bother gonna compare it to the various others.
3) Hammer of Sigmar. Re-roll 1's to hit or wound during the combat phase. If this is *both* to-hit and to-wound rolls I'd consider it one of our best, if not our best prayer. This Prayer is pretty much on par with many buff spells from various lores.
4) Battle Howl: +D3" to charge. Doesn't increase max charge range and doesn't add any M-value so useless unless you charge, so it's kinda mediocre. Comparable spells would be the +1 M/T/I from Daemonology and +D3 M (or even WS or I if you roll high enough) from Lore of Undeath.
5) Winters Chill. This seems really good at first glance, but if you do the math on it, it's inferior to most defensive spells out there + it only works in close combat. If your opponent hits you on 4+, it's the equivalent of having a -0,5 to hit (instead of just flat out -1 to hit) and if they hit on 3+ it's even worse. This prayer does shine against Poisoned Attacks, but other than that, it's a *really* bad version of Glittering Robe.
6) Wrath of Winter: This prayer, just like Hammer of Sigmar, isn't half-bad, depending on how you apply it + it's (strangely enough) not restricted to close combat only. There are no comparable spell, altough I guess at the end of the day, most of the time a spell that grants +1 Attack or similar would be a better option against most targets.
So that leaves 2 decent/mediocre (Wrath of Winter, Hammer of Sigmar), 3 weak* (Shield of Faith, Winters Chill, Battle Howl) and 1 garbage (Soulfire).
(*Weak as in, they are more or less bleak copies of existing spells/abilities.)
All in all, the prayers aren't terrible, but just as with the Empire army as a whole, they leave alot to be desired...
