I can only comment on Eriu from like turn 33 or so, since I took over for Samhain. He still looks at this thread and may comment on the earlier life.
Eriu had several things going for it at my takeover.
Great research
Good income
Good gems
NAP with Pan
A Sidhe Lord and champion every turn along with a Tuatha was being recruited every turn.. A very minimal amount of non commanders was being recruited as well.
I created two distinct undead armies based on heat and cold. These were supported by Sidhe C/L and Tuatha. More or less, the undead armies were damage sponges while the mages did their things. I was going to create a poison army but it never happened.
Going for Arcos cap, All who could buffed mistform. I used a D4 mage to cast darkness, equipped all my non-thunderstrikers mages with bows of war, set them to eagle eyes and fire closest. I had another mage cast wind guide, another cast arrow fend, and my pretender, who was a rainbow crone, to cast fire arrows. All other mages were set to eagle eyes and spam thunderstrike. Since Eriu gets 50% darkvision, this really tore Ulm up, especially the trolls..... all those poor, poor trolls.
My army used about 70 mages and 150 or so troops.
After taking over Arcos cap and the surrounding lands I headed on towards 46, 47, 42 enjoying good success until dragons ridge. I had split my army off to grab more land while seiging dragons ridge when Ulm broke seige. With most of my good guys out, he attacked with a very potent army that devastated mine and even killed my pretender. I lost count of the number of master smiths he had that seemed to spam magma eruption.
While the above was going on, I sent a small force of hall of fame, heavily equipped tuatha through the south and into Ulms backyard. I found lots of nice gem sites and was raiding at will, destroying anything that they met, except for troops on forts. I tried to lure Ulm out using glamor and hiding and sniped a few troops but for the most part he stayed put. I cloud trapezed more tuatha in for a total of 10 thugs. This is when i i Had Ulm down to the mat. I think he had 11 provinces left but of course, 9 forts. I could not siege them with what I had and thats where the southern group ran out of steam. I wish I was able to give them some siege weapons, but I couldn`t at the time.
After the defeat at dragons ridge, I sneaked most of the surviving mages out and around Mans area while running a non glamoured suicide force to distract Man. Any troops that went to the West sneaked through and joined my southern army near Ulm which brought them up to 17 thugs. I`m confident at this point that the southern group could stand up to almost anything currently on the map. Over half are in the HoF and the rest were at 3 stars.
Man started doing the raiding in my area and I watched in horror as my unrest started to skyrocket. At one point Arcos was at 350 unrest.
I ended having to set just about everyone on patrol and cast watcher in many provinces, which gives a patrol bonus of 50. That helped at the end, and most of my provinces were back at zero unrest.
I hope I answered some questions you may have had and please ask if you have anymore or need more details. This was like my 3rd MP game in public, had a few private ones at work, so this was a good learning game for me as well.
I really think the success I had was due to the magic cap at level 6. I don`t think Eriu is a powerhouse at end game.
Short Version: Thunder Strike kicks butt.