Yea, kinda. Lysithea pays for that in having the lowest total growths and being as tough as paper mache. Priscilla as far as I recall wasn't all that minmaxed and that's the point: we have an actual character to base it off of, so if we're putting them in three houses, we should be as faithful to the character as possible.
A lot of the abilities characters have are more around what makes sense for the character than what is 'optimal' or 'novel' even ingame. That's why every physical unit isn't running around with battalion vantage-battalion wrath despite the fact that everyone wants that combo for their chosen creation because they can't bear them being suboptimal.
OK quickie one with explanation:
Robin male or female doesn't matter:
Base 29 9 8 8 9 6 9 6 6 (total 90)
We're doing this quick, dirty, and lazy. We take the base stats of Robin without accounting for any variation of flaw/strength and total them up. We throw this through a ratio calculator using the same stat total as Byleth minus his charm stat (total 83). We get some basically workable numbers for a "hybrid" type character. We use our remaining "points" to return to 90 and give Robin 6 starting charm; fitting for an avatar/non-lord Amnesiac. Note that defense is oddly high showing that this strategy is not perfect.
Growth 55 45 40 40 40 45 30 25 50 (total 370)
Since we're using a robin base with no asset/flaws, we end up with a very middle of the road character. Because the health to stat ratios in awakening are so different we see that the health was far too high and cut that growth down some (already done) and give the remainder to charm. Robin is an excellent tactician and thus This is referenced in his higher than average charm (though this could be done in better ways) He is also the avatar of a fell god and only an amnesiac rather than devoid of emotion, so the higher avg charm fits.
Max 107 54 54 54 54 60 54 54 63 (total 553)
From here on we can't really use Byleth's totals as a base anymore, on one hand you could and simply keep the 99 charm but I'd rather this as a recruitable unit rather than literally replacing the unit role of Byleth. So we use our next hybrid character Ingrid. She has the same growths as Byleth and ~7 less total base stats. The problem is that we still have Robin using the Avatar/Lord level base stats. Simply using Ingrid's totals would drop the magic/str ratio abnormally low so we'll simply cut away a little as we had done with the growth rates.
New Base 26 9 8 8 9 6 6 6 6 (total 84)
We cut 3 from base hp and def, putting them more in line with the other characters and can pretty much call it good. Their max stats aren't insane, and are in fact oddly equal and yet I don't find myself minding all that much. Notable for their abnormally large health, though not to the extant as Raphael.
Since Robin canonically bears the Mark (read: Crest) of Grima, I will, despite how much the overuse annoys me, give Robin a Crest. Rather than reusing one of the standard effects, I look to Bernadetta and Dimitri for inspiration and precedence. Their abilities each could allow for essentially a doubling of the usual damage or more and thus I feel a bit more safe to simply adapt Ignis as a crest ability. so:
Crest of Grima (Major)
When using attack magic, Occasionally add 1/2 str to Attk.
When using weapon attacks, occasionally add 1/2 mag to Attk.
Activation % 20 (major) 10 (minor) 5 (Item)
At the beginning its actually weaker than Felix's crest only adding 4 damage for a lower frequency, naturally as time goes on it rises in strength to Dimitri and Bernadetta's level but is more frequent due to have to activation conditions (magic or might) and having the major rather than minor activation rate. Robin gets major only because they are the avatar of Grima perfected by the Grimleal, Morgan would only have a minor crest. Still a bit more powerful than I'd like (I think) but I'm not exactly going slow and steady here.
Personal Skill: The easy and obvious one is to give him bootleg professor's guidance known as Veteran. Alternatively just give him the discipline skill.
Personally I'd prefer giving him a weaker variant of his rally spectrum skill (Shamir has this essentially as a self rally) as his personal or a modified Offensive tactics to illustrate his superior ability to tip the scales. The final and more OP option was to double his gambit uses.
For Reason magic its actually rather easy:
Thunder Thoron Death Dark Spikes
The first two can be considered robin's signature spells and the last two represent Grima's powers as Death is visually similar to Grima's truth and Dark Spikes is similar to Grima's attack.
Faith gets a bit trickier and thus more limited. I was half tempted to go all out and cheese with warp and rescue but instead decided more conservative for Aura and Abraxas since Robin will already be struggling with mixed black/dark magic.
Since I haven't mentioned it robins strengths would be no flaws with a strength in Reason, Swords and Authority. Normally I'd be tempted to give them a hidden talent in faith (giving them faith uses x2 or avo +20) but at this point hidden talents are so overused that I'll leave it as is.
With a strength in authority Robin would be loaded with rally skills, finishing with rally movement being the third unit to have it. The battalion skills would be vantage and desperation as they fit Robin's mo of outmaneuvering the opponent. What rally skills he would have otherwise, I didn't decide.
I don't really need to go on, with his balanced stats and growths most classes should push him any direction needed and magic or strength will never be a completely wasted investment thanks to his crest and lack of flaws (in proficiency) The unit ended up the way it did due to the choices made by IS in awakening rather than my trying to minmax a character hardly faithful to the original. The female version is probably OP.
Canon classline is dark bishop/warlock, if you care. Unique outfit should be obvious.