Spirithost is a solid early game option, though one that we're really not going to want to take past 40. Can sometimes be 50 if we're really desperate. She does have a few issues.
One of which is that remove debuffs/block debuffs is on a 5 turn cooldown and the other being that the speed aura is a small one at 10%, which will get outclassed by High Khatun once you someone gets her. Overall, the speed aura is solid and the increase attack is the best part of the kit. She doesn't really lend herself to account progression, though. You will end up being much more likely replacing her in a team before you will Warmaiden just based on needing to fill those team spots with champs who do more than Spirithost does.
Warmaiden does get outshined by the good defense down epics but there aren't so many that I would rank her below Spirithost as best farmable rare. Warmaiden isn't really meant to be a nuker so much as your defense down that you take up to 50 - and not past, in my opinion - who you'll pair with your DPS (starter and Ronda, these days) to clear waves in dungeons and campaign.
Having a 60% defense down on a 3 turn cooldown is quite important and even though I think Warmaiden will eventually get replaced as most players core defense down option, she does the job well enough early on.