Will there ever be any flat stat boosts?

Probably not, and if they do it'll probably be way down the line.

I think it's something to do with changing the value of already released content. Something about laws behind digital content released in gacha games in Japan, or something.

I feel you with Jaffar, dude was super fun to play in FE7 and hurts to see how bad he got shafted in heroes.

The refinement on his dagger is probably the closest thing we'll ever get to IS buffing heroes. I doubt they'd ever add a flat stat increase to units because it could potentially screw over players who dropped thousands of dollars for a very specific niche (Think +10 +spd windsweep Hectors) It sounds weird I know, but I guarantee you that there would be a very vocal backlash if IS started tinkering with statlines, no matter how small.

They've got a formula for the BST of each unit. Jaffar's BST at 147 is about the same as other gen1 ranged units. It's not cos he's a dagger user that he's got bad stats, he has a lower BST compared to melee units because he's a ranged unit. Bow units suffer the same penalty. His BST isn't the problem, it's how they've been distributed on him. His hp is high and the rest are just too balanced.

Spring Kagero is not that special, she have a better distribuition of stats and a weapon with much more might.

>Talking about Jaffar getting shafted

Yea, that much is true, but...
Let's avert our attention on units like Henry and Odin. Mages are one the most overpowered unit types in this game at the moment. Yea, daggers units are a little lack luster in general, Sothe and Spring Kagero at the moment being the exception, but at least their own class didn't betray them. They have what most dagger units should posses, decent power, and high speeds.

Henry was a dark mage with high power, above average HP, high defense, average speed and middling resistance at best. They only managed to get his defense correct, so if anything else, Henry got brutally and utterly shafted among a handful of other units.

If they wanted to give stat boost to units, they should actually hand out the stat boosting items found throughout the series, but... then that would be a problem since most powercreep units would be even more powercreep. So it would be a losing situation anyway.

Dude idk, my Jaffar has a 44/42 offensive spread... He can't blow away tanks (even with his amazing chip), but he can zonk more than his fair share of the roster. Especially with a dancer.