Generally I agree with your assessment but Fiona kind of throws a wrench in that logic. You have to baby her and give her stat bonuses items to make her good.

The growth rates of Zihark are along with the worst of the swordman of Radiant Dawn,  Lucia has the worst of all swordman.
As far as i know Titania was considered Jeigan in FE9...and Sothe in the first chapters could fall in the same category,  but that is opinion the sames as could be talk about no Jeigan character in Radiant Dawn

Zihark only starts with a base of 30 hp, which is rather low for a already upgraded Swordsman.

As things stand now, I'm in part 2. My end art one Eddy was 20/15/0, considering I have upgraded my other unit(the axe guy) to a 20/15, and Michai(leader) is 20/1 as well, and I still have a master seal in the bank.

Not bad. I used the double exp and made sure to be very careful with each experience point and not waste them on units like Jill, or the Priest.

I ended up with two VERY strong characters, much stronger than Sothe, in Eddy(maxed str and hp) and Axe guy, and a level 20 Michai(dunno her name, lol) with maxed magic and resiliance.

Zihark is also quite a formidible member of my part 1 team, and I did level him, but kept him mostly in the back for reinforcment cleanup.

Zihark in PoR was probably my toughest character, sans the end game characters you get for free.

Eddy, as expected, hits really hard and has a long movement range, and dodges a lot, but takes a lot of damage when hit, and has a low HP due to his class though it is maxed.

I junctioned an ability that regens his hp after each turn, which has helped make him a very self sufficient unit, but I still have to watch out for spears and mages, which means he's not the elite destructive unit that I wanted him to become.

For my money, the most killing unit in my part 1 was the axe wielder dude, upgraded once, then Eddy, then Zihark, then Sothe, Jill, and Mikhal(lol?).

I like Eddy better for part 1. Why? Xp.

1) I attack one enemy with Eddy
2) he takes 60-70% of the enemy HP and loses 40% on the counter attack
3) I use sacrifice with Micaiah
4) I heal Micaiah with Laura
5) I use Nolah, Jill or other usefull unit to finish the enemy and get the remaining xp

With Zihark I would 1 hit ko the enemy get some shitty xp (because his level is much higher than the rest of my units) and lose the opportunity to heal.

Average stats at 20/20/20 (Edward <> Zihark)

HP 55 > 53
STR 32 > 31
MAG 8 < 13
SKL 40 = 40
SPD 40 = 40
LCK 30 > 25
DEF 26  > 24
RES 16 < 24

With the exception of Luck and Resistance, they're within a matter of points of each other.  Zihark may have lower Luck but he has Earth affinity which not only boosts his avoid way higher but also that of another character.  Edward, meanwhile, has nothing on Zihark's resistance.

Jill was frustrating to use at first because she couldn't hit or OHKO anything.  I'm glad I stuck with her though, she turned out excellent (though I'm sure I was quite fortunate with her growth).

IMHO, there's no point to using any of the prepromoted units in Part 1 except for in one map where you are forced to.  They're not bad later on, but if you play well you have every character (minus Fiona) at 20 or better by the end of Part 1.

Finished part 2. That battle took 2 hours, I must suck in this game.

No, you're fine.  Part 2 is really short, but its battles are really really long/huge.