Always nice to see discussions on Jomon
It is one of my favourites although a poor 'power' pick in mp.
I think that Jomon has poor SC access. It has no blood or death access via its national mages. Nor much flexibility on its pretender to get around this. While you can boot strap in to either this is hardly what anyone would call good access, every other nation can do this. It has some reasonable death thug summons before the Dai Onis (summon 8). But you are unlikely, as you are boot strapping, to get these early in numbers and death has plenty of such summons in any case. Dai Onis are all but impossible for Jomon to cast and are pricey both in Death gems (45!) and in that they have a price (500gps but sacred) so cost a fair whack each turn in upkeep. Unlike most summons.
Jomon is a slow starter and this is its real problem, regardless of whether you think its troops are poor or merely average. It's starting army is miserable. Probably the worst in the game. It can't even take on a LA strength 5 indie. It's troops are very resource hungry so you can't mass them early. Even with Production 3 (and few of us like to spend points on Production) you can't mass troops quickly early on. You can struggle to produce enough to cover losses in the initial turns. And without neighbours adding their resources even waiting a turn or two won't give you that critical mass to take indies with few/no losses. For this reason I think Jomon needs an awake Pretender to help with expansion in mp.
While Jomon has access to the Wrym and Cyclops for that fear/awe awake SC combo neither give the initial boost in to death that you want to make boot strapping in to that easier. Therefore what you want, more than any other nation I can think of, is the Prince of Death. But you can't have him. So I agree with Kissblade that your best choice is usually the Ghost king. But because I think you need him awake you need to sacrifice his magic (or your scales) to get the high Dom for awe.
You can of course give him lower dom and keep reasonable scales and give him some extra magic (paths just 20 so this is efficent). This makes him merely a thug. But that works quite well if you combine him with your initial army. Your samauri LBs can shoot through him as he is etherial. You will at least be able to take one province a turn that way
Not a great return for an awake pretender but better than what you will do without.
If you do go Ghost King I would definitely add one blood to him. Even if you are not going to try and boot strap in to blood. This enables him to get in on a communion later via Sabbaths without the risk of having low astral. It also gives him something to do when he no longer cuts the mustard as an SC. Blood magic isn't all that great on the battlefield but your Ghost King can be a fine addition to a Jomon Communion. It will give you communion boosted death and blood on the battlefield including that nifty fatigue reducing blood spell. You could produce a few surprise moves with it. Your opponent may not expect you to throw down darkness (and mist / storm) followed soul slay/mind hunt rather than the usual wind guide/flame arrows on your masses of Samauri archers. Could work well against another archer heavy nation as your Samauri LBs will stand up in melee.
There are a few other niggles with Jomon making them weaker than they appear. A cap of 2 on astral means you can't reach the rings without empowering. A big annoyance. Although giving 3 astral to your Ghost King (nice early buffs then retire him to be a forger when low astral is too dangerous) could be worth it.
Your mages not only have 1 map move but just 8 hps also. Meaning they are especially vulnerable to Earthquake and such like. Most communionable mages are vulnerable to such things but Jomon especially so. Makes using large communions especially risky.
Your mages are great forgers with their path options. But you lack the thugs/SCs to kit out without a lot of work. But they do struggle to build boosters as they have variety rather than the high Astral, Air or Fire needed for those boosters.
Re the mages I think the Master Shugengas are underrated. I have had more luck than Archaeolept in getting an E3 on Master Shugenga although I haven't worked out the probabilities. I like to recruit a few early in the hope of getting one early to build hammers. Hammers are construction 2, while earth boots are Con 4. There is plenty of stuff at Con 2 that can be built cheaply and enhance combat mages and your Ghost King without investing in the research for Con 4. E3 and N3 MSs fit very neatly with an easy to forge communion crystal into the Jomon Communions later. Making high level nature and earth battle spells easier to cast.
I do like Jomon a lot but I definitely think it is weak in mp. IMHO it has poor troops, lacks the one pretender chassis it really needs (so poor picks for the nation), poor SC options (as poor as any other nation - everyone could boot strap in to Death or Blood - and Jomon can do neither naturally or afford a pretender that can cast summon any elemental royalty or Tarts or bloods easily). It has good mages which are recruitable everywhere. But they do have weaknesses. Plenty in fact.
But its main weakness is at the beginning of the game. If you are alive and in decent shape by the mid game you can mass your troops via multiple forts (even with sloth scales), you have easy access to communions and hopefully should have been able to boot strap in to death or blood. The mass buff spells work well with Jomon and are easy via even small communions to cast. You lack thugs/SCs but this is hardly unique to Jomon. And there are even more summons available now to Jomon, some she can even cast
In sp Jomon can be a blast to play as there are a lot of options with its range of summons and magic variety. But I think Jomons very weak early game makes them poor in mp. Diplomacy and luck (in neighbours and surrounding provinces) are often more important than nation strength. But so what, Jomon is still weak. And by being weak the early game can be a mindfield diplomatically.
It would be easy to fix, there is no need to radically change the feel of Jomon by adding death or blood to its mages. Or boosting its troop stats. Although I do like that the devs are looking at and adding options to some existing nations rather than just adding new ones. The more of that the better
For example why do you get such a small starting army? Why not at least 15 of each? Or even better swap the Ashigaru for Samauri and give them 15 of those with 15 Sam LBs. Then Jomon could use its initial army to expand as most other nations can and an awake SC would then be an option rather than a necessity.
Even simply giving the Prince of Death as a pretender option would be a huge boon. PoD is 45 cheaper than the GK and thanks to higher base dom gets awe for 49 (I think!) less. Thats two scale shifts or extra magic. Plus it has more base death magic (3 v 1). You give up etherial for flying and decent fear. Its a cheaper and in most cases better SC chassis. Apart from Jomon who even uses the Ghost King as an SC?