That's basically my point, yes. As constructed, having two stats that only contribute offensive scores are too polarizing.
My "scrap Luck for Intellect stat" proposal seeks to address these issues. The root of the problem is that Strength and Magic, traditionally, contribute nothing to units who don't use the stat for offense. Thus, hybrid functionality becomes nothing more than a neat trick.
One solution from IS was to use Str as a weight buffer in FE9/10; magic classes really want this, since their Constitution scores are typically lower. Mages would appreciate a low-growth weight buffer, but this consequently makes the stat too overpowered for physical units. Keeping Constitution as a constant for physical units, while splitting magic weight between Con and Str, allows us to have the best of both outcomes without the downside of either.
The way I've done it, splitting weight calculation into separate physical/magical formulas, gives added purpose to Str for only mages (physical units rely more on Str than mages do on Mag), and adding Dodge to Int gives that stat a multi-functional purpose. Unfortunately, the stats were seemed of relatively little value to classes prioritizing the opposite offensive stat.
Attack speed itself seemed too powerful; such that it either had to be an independent stat, or divided amongst two. Skill gets its necessary buff by splitting AS, while Speed gets a nerf. Two birds, one stone. However, that made Skill a little too good, relatively, so it seemed ideal to take away the x2 multiplier it gets in the accuracy calculation. With attack speed and avoid formulas already split into physical/magical, adding accuracy into the mix didn't seem like too far of a stretch.
Spirit also factors into avoid in Luck's place, which buffs the survivability of healers and mages to a lesser degree. It shouldn't be a major change, since high Res classes typically got characters with high Luck growths, but consolidating that function helps make this stat more relevant for physical units (who, in most cases, would be better served trying to avoid magic attacks than tank them--Spirit helps them on both fronts).
This is, I suppose, the point where things get complicated. Mainly because I broke the "rule of two" (any component, ideally, should only be impacted by two stats at the most). Physical units get increased hit, crit evade, and magic weapon damage from the Intellect stat. Magical units get a 1 point of weight buffer for every 2 Strength, which in turn helps their avoid, and they get half of Str added to hit. Then, the opposite defensive stats for each factor into hit as well (part of good defense is consistent offense, after all); half of Spirit to physical hit, and half of Defense to magical hit.
Yes, I've broken the "rule," but incorporating all four of Str/Int/Def/Spi, plus Skill, means that all of the main stats sans Speed are, at some point, factoring into hit. Perhaps this part is too complex; but if complications are necessary (which I think they are, in this case), asking a player to remember that their opposite offense/defense stats factor into hit is less cumbersome than many possible solutions.
However, I also understand that these would be significant changes in several respects. Part of the appeal to Fire Emblem's handling of magic is that it functions exactly the same as any other weapon, and my proposal complicates things inherently by changing that fundamental fact. At the same time, there isn't enough capacity with the system as constructed to make the Str/Mag split work, which necessitates an innovation like splitting formula into physical/magical variations.