That all sounds plausible enough, but it breaks down in many situations. For example, units with low CON relative to their weapons (Such as Peg Knights and some Myrmidons/Thieves), and who also really depend on avoid for survival, need extremely high SPD for that stat build to work. Like, enough to hit their un-promoted cap before 15/-- in many cases. Florina and Fiora would suck much less as fighters, even given the fairly slow enemies, if they had 80% SPD growths. Also, while a 30% growth in that area my be as good for said units as 80% when it comes to fighting Brigands, if you want anyone who can reliably double Mercenaries/Myrmidons/Nomads and their promoted counterparts throughout the game, such high growths may be necessary unless your faster units have bases on par with someone like Rutger or Raven.
by the way i really disagree with growth differentiation and all that other bullshit
if you want a unit to grow into a strong, fast, etc. unit, then use a high str, spd, etc. growth by all means. but if you want a fast unit to stay fast, or a strong unit to stay strong, you don't need to heap on a 50%+ growth on top of an already good base. that just widens the statistical gap between classes when the gap should already exist in the class bases.
example: if swordmasters have 13 base spd and warriors have 9 base spd, then you don't need an SM with 70% spd growth and a warrior with a 30% spd growth to convey the point that SMs are fast. the swordmaster will always double the warrior even if they both had 30% spd growth. similarly, you don't need to give your general a 50% def growth because that very quickly outpaces the enemies' atk growth (keep in mind that you're also growing HP on top of that). enemies have 50% str growth maximum (fighters) and also level up very slowly. unless you want your general to be an invincible juggernaut that requires no brain for a casual player to use, then consider using a 20% def growth or lower.
also consider using lower HP growths in general. the only weapon upgrades that enemies get are iron -> steel -> silver, with typically a 7 MT gap between iron and silver. that's like, a 14 HP difference over 2 attacks - and really, your typical character should be getting 2-3RKO'd unless he is bulky in some way. so you ideally want to be growing ~14 HP over the course of the entire game for a character that exists during the entire game.
the truth is that you should not be looking at existing fire emblem games as a good example. a lot of the time, they don't get it right. you have SMs that double everything and dodge everything and dracoknights that shrug off physical damage on one side of the spectrum, and growth units that don't really grow fast enough or well enough on the other side of the spectrum.
On durability, keep in mind that the number of enemies you are expected to tank on enemy phase has a tendency to go up as you get further in the game, so unless you want to trade quantity for quality on that front, defensive growths that at least slightly outpace enemy MT increases is a good idea on units that need to take hits. As for HP, the fact that it needs to be increased by huge quantities in order to make a difference for all but the most frail (Mostly healers who need to avoid being killed in one hit) is an argument for higher variations between different kinds of units, not less. In most cases I would recommend just jacking up the base if you want someone to be notable for high HP, especially for the "pin-cushion" defensive build common to primary axe users, but if you must do it through growths, seriously consider going well above 100%.