In Shadow Dragon & the Blade of Light, promotion gains consist on giving the character as many points as necessary -the "x" value shown in the table- to reach the promoted class' base stats. If the character's stats are higher than their promoted class' base stats, they will not receive any bonus.
Analysis
This character analysis section may not be accurate to every player's experience.
Of the six Mercenary- and Hero-class party members in Shadow Dragon & the Blade of Light, Radd has the strongest growth rates, but gets off to arguably the weakest start. His low base stat values in HP and Strength hurt him, but high growths in both stats make it likely that these weaknesses will abate if Radd is given the chance to level up. Ogma, Navarre, and Astram remain superior infantry swordfighter options overall, but Radd is fully capable of catching up if the player sees fit to invest in him.
In Mystery of the Emblem, promotion gains for HP and weapon level consist of giving the character as many points as necessary—the "x" value shown in the table—to reach the promoted class's base value. If the character's value for one of those two stats is higher than their promoted class's base value, they will not receive any bonus in that stat.
This character analysis section may not be accurate to every player's experience.
In Shadow Dragon, Radd fares significantly worse than in the original, being one of the weakest characters in the game. He has subpar base stats, a poor weapon type, and faces heavy competition from Abel, Cain, Hardin, and Frey for any potential spot he could fill by reclassing. Even if he opts to stay a Myrmidon, Navarre joins five chapters earlier with higher base stats across the board, and a higher sword rank that enables him to use the Killing Edge to bypass his low Strength. His growths are only average at best, and the effort required to raise him to any level of self-sufficiency far outweighs the payoff for doing so. As the investment required for Radd to catch up with other characters is unlikely to be worthwhile by any objective metric, he is best left on the bench by those seeking to play optimally.
In Shadow Dragon and the Blade of Light and Mystery of the Emblem Radd's characterization is practically non-existent, but his ending at least shows that he harbors romantic feelings for someone, and that he is willing to put aside his life as a mercenary.