Okay. I've been thinking about it, and this is the best I could figure out for a replacement for Nate.
Maya Amano (3.0-3.5?)
Stat build: Average, all stats. Sooooooo not worth attempting to incorporate a stat build setup into this.
Note: All healing/damage percents are when you get them. Maia Custom is still usable endgame, which is more a testament to Maia Custom.
Persona:
Floor 1: Maia (Hama (ID, Holy, ST, 36% chance), Dia (40% healing, ST), Aqua (25% Water damage, ST), Media (45% healing, MT), Multi Dimension (ID, non-typed (not phys, not magic), 20% chance)) - High Tec, Spd, Low Str; Immune Holy/Dark/Status
Floor 2: Tengu (Maha Garu (~30% Wind damage, GT/all), Gry (25% Almighty damage, GT/All), Iluzone (52% chance to blind opponent (drops mag/phys accuracy to 1/4th)), Wall of Air (Entire team immunes 1 Wind attack), Recarm (Revive with 50% HP), Blade of Fury (15% Sword damage, GT, physical)) - High Tec, Low Vit, Reflect Wind, Weak Earth
Floor 3: Maia Custom (Replaces Maia) (Hama (ID, Holy, ST, 36% chance), Invitation to Sleep (Sleep, Nerve, GT, 52% chance), Scratch (20% damage, Strike, physical, ST), Maha Aques (55% water damage, GT/all,) , Medirama (~90% healing, MT), Multi Dimension (ID, non-typed (not phys, not magic), 20% chance)) - Very High Tec, low Vit; Immune Holy/Dark/Status
Floor 4: Genbu (Paralyzing Bite (15% damage, 52% chance of causing Sleep, physical, ST), Wall of Earth (Team immunes 1 earth spell), Raku Kaja (Double one allies' physical defense), Magdyne (50% earth damage, ST), Maha Magdyne (55% earth damage, GT/all)) - Very High Vit, Low Tec, Spd, Void Earth, Strong Ice, Lightning, Nuclear, Weak Wind
OR Byakko (Bite (20% damage, physical ST), Suku Kaja (double one allies' speed), Blizzard Breath (30% ice damage, 30% chance to freeze opponent, MT), Wall of Water (Team immunes 1 water spell), Acid Rain (40% water damage, MT)) - High Str, Agi, Low Tec, Vit, Immune Water/Ice, Weak Fire
Floor 5: Tsukiyomi (Sama Kaja (Double an allies' magic defense), Maka Kaja (Double an allies' magic power), Zandyne (60% almighty damage, ST), Magic Seal (Mute, GT/All, 24% chance), Mudoonn (ID, Dark, MT, 48% chance )) - High Tec, Immune Earth/Holy/Dark
OR Genbu OR Byakko
Floor 6: Maihime Amano (Affectionate Prayer (75% healing, MT), Dance of Protection (Double one allies' def/magic def)), MASSIVE Tec, Low all other stats, immune water/holy/dark.
AND Artemis (Bufudyne (45% ice damage, ST, 50% chance of freeze), Hypnotic Wave (Sleep, MT, 44% chance), Absolute Zero (35% ice magic, GT, 30% chance of freeze), Diarahan (Full heal, ST), Crescent Mirror (65% almighty damage, MT)) - Average stats, Reflect Magic, Weak Physical.
Advantages: Versatile mage, with healing, buffs, and damage!
Disadvantages: Doesn't get full revival, is almost always physically less durable. Some of her better skills require switches to worse Persona.