Having a combo throw is often more important than having a kill throw, especially because Samus' gets her more than 30% which is a lot for a combo throw in this game. Look at characters that don't have kill throws like Sheik and ZSS. They have their combo throws that act as kill setups for them rather than just killing outright. Combo throws, in this fashion, beat out plain old kill throws any day because they're multi-useful. If Samus' actually confirmed at percents higher than 50%, it'd be a downright powerful throw.
I think the question of whether or not lag reductions on her grab should or should not be number one priority, I think it's clear that lag reductions are, in fact, number one priority. Having a safe grab is what makes a lot of good characters good. Making Samus' safer only makes her better. Going for grabs more often, because she won't be getting punished for literally every single one with partially charged smashes, allows her better opportunities to rack up damage, getting characters to kill percents earlier, and shifting her focus to killing before the opponent which works out well in her favor as opposed to the other way around since she doesn't have the kill options of a lot of other characters. Again, a combo throw that actually worked better as a kill setup would aid this as well. Not a kill confirm grab like pre-patch Diddy or Luigi, more like Sheik and ZSS.