Vanessa’s main advantage over Franz is flying. Some examples:
-In Chapter 2, Vanessa is the only one who can reach Ross before he’s killed. w1n. Ross and Garcia may not be the best units, but whenever they’re used, you have to use Vanessa to get them, so that’s a point for her.
-In Chapter 6, saving the NPCs beyond the mountains nets you an Orion’s Bolt. Vanessa can cross the Peaks, no problem, but no one else in your army can. The only other way to get the Orion’s Bolt is to have Seth rush the boss, but that leaves a lot of kills on the map that your team could have taken, meaning you lose out on a lot of EXP--even Seth himself is lucky to get one level from that tactic, since his EXP gains are also very low--so that’s obviously an inferior idea.
-In Chapter 9 on Eirika’s Route, there’s a Rapier, a Dragonshield, and an Angelic Robe that Vanessa can get you from the villages, and also a Speedwing with Amelia (since Colm can’t reach her before she leaves a lot of the time). There’s also an Ocean Seal on one of the Pirates in the middle of the sea, so w1n for her.
-In Chapter 10 on Ephraim's Route, there's a Secret Book on a Fleet that requires a flyer to get. Tana, at this point, is OHKO'd by the Fleet, whereas Vanessa can take a hit from it and one-round it. Cormag starts clear on the other end of the map, and he isn’t even on your team initially, so Vanessa’s basically the only option here.
-In Ch. 17, Syrene will be easily killed by the Druids surrounding her (or, as an NPC, she'll drain EXP from your team by killing them, if she somehow survives). Vanessa is one of the units who can recruit her, and seeing as Vanessa flies and has high mobility, she's obviously going to be the one doing this. Syrene comes with a Silver Lance, so ftw.
-In Ch. 18, the Gorgon eggs hatch very quickly, and Gorgons are both more dangerous than Gorgon eggs and give less EXP, so your flyers are pwn here. Vanessa w/Javelin >>>>>
Those are specific examples, but there are easily more general applications of flying. What about the huge mountain range in Chapter 12 Eirika? Or the big expanse of ocean in Chapter 11 Eph? Or the massive river in Chapter 17? Or 15 Eir/Eph, with the vast desert? Or the woods and mountains in Chapter 20?
And that’s still only noting the most prominent obstacles. Vanessa wins mobility against Franz even when those huge ranges of obstacles don't exist. Prepromotion, they have the same Movement, but Vanessa can bypass Forests and Mountains, and postpromotion, Vanessa has two more Movement, isn’t hampered by a horse mount (which gives Franz _less_ mobility than the average unit), and continues to fly, so she has a massive lead there.
Even without considering any of that, just the items she gets you alone give her a huge advantage. Orion’s Bolt, Speedwing, Secret Book, Silver Lance, Dragonshield, Angelic Robe, Rapier, etc. are all very useful items—even if you don’t use them, you can sell them to get money and buy weapons like Killers, improving your team’s offense by a lot. Vanessa has a huge lead over Franz thanks to this and Franz has no viable answer.
Then, statistically, they compare about the same.
15/0 Vanessa (A Lute/B Moulder):
14.9 Atk, 18.9 AS | 24 HP, 74.5 Avo, 13.8 Def, 14.2 Res
15/0 Franz (A Seth/B Gilliam)
16.6 Atk, 14.0 AS | 31.2 HP, 48.1 Avo, 14.5 Def, 8.8 Res
Vanessa wins offense against fast stuff and Franz wins offense against stuff that they both double. Most things fall into the latter category, but it’s not a major victory for Franz anyway (the AS lead definitely matters, and the Atk lead is still only 2 against most things and 3 against Axes).
As far as defense, 26 Avo and 6 Res vs. 6 HP and 1 Def looks to be a pretty clear win for Vanessa against pretty much everything except for Axes. Bow weakness closes the margin by bit, but at the very worst it’s as small as the offensive gap, so meh, w/e.
Later . . .
20/6 WK Vanessa (A Lute/B Moulder)
20.4 Atk, 24.9 AS | 32.0 HP, 92 Avo, 16.8 Def, 18.2 Res
20/6 GK Franz (A Seth/B Gilliam)
22.6 Atk, 20.9 AS | 42.2 HP, 65.9 Avo, 19.0 Def, 11.8 Res
Offensively, same again. Vanessa wins vs. fast enemies, Franz wins vs. other stuff, so Franz wins overall. Meanwhile, on the defensive frontier, 10 HP and 2-3 Def don’t even compare to 26 Avo and 7 Res, especially when Vanessa’s Avo is so h4x (she’s basically untouchable against most things).
Franz can snag a win against Axe enemies, but against everything else he loses clearly, and most notably so against Magic. Bow enemies . . . don’t really even hit Vanessa anymore. The most accurate of them have around 90 Hit, and 92 Avo cleans house on that quite clearly, even if you apply an Avo loss from wielding Steel Lance or something.
As you can see, throughout the game, Vanessa is winning durability pretty consistently, whereas Franz is winning offense. Neither has a huge victory—clear victories, sure, but the margin is never big enough to be considered decisive for either side. Indeed, by far the most notable advantage that exists is Vanessa’s flying.
Franz may win against her earlygame, where she doesn’t yet have her supports and her Bow weakness actually matters, but that’s the only time that it’s clear at all, and, unfortunately for Franz, earlygame is also the portion of the game that counts for the least, since the enemy concentration is so low and enemies are so weak (to compare, the first five chapters of the game are similar to LHM in FE7, phail—the only decent one is 5x, and Franz isn’t even in that, so meh).
Comparing pretty evenly in stats + flying + additional mobility (2 Move postpromotion + no mount restrictions) = Vanessa is the winner.
OBJECTION!
Ergo, this is completely irrelevant to the case. He's using outdated stats. I ordered in some new stats and it clearly shows that Franz is superior. Amateurs.
Unfortunately for you, Fire Emblem has a static interface. You can make basic changes as you play, but changing the actual growths and bases without a ROM or hacking device is almost impossible, and even if you did manage to change the stats, you could apply the same treatment to Vanessa as well, so it doesn't change anything.
w1nn4r = b4n3ss4