1. Those 3 start out at much higher levels than the others. The only Laguz that can hope to catch up is Lethe, but then she has lower base stats than Ranulf. And yes, there are people who don't use the Royals but it still doesn't change that while previous FEs might've thrown you one super unit near the end to save the day RD gives you 4 of them.
Given that your team is split into 3 pieces in Part 4 that's kind of a necessity to prevent first-time players from screwing themselves over, something which RD runs a fairly high risk of as it is. Not to mention the sheer insanity that is Dheginsea.
And believe me, I've Bonus EXP'ed the hell out of Lethe. She's competent, but even among the non-royals, there are better laguz.
2. Volke is only slightly better than a Whisper
Yes, and I'm "slightly" obsessed with Yoshi. He's still far more viable. 4 extra strength and +25 critical means a lot on a character who should be double-hitting virtually everything. Then of course there's the fact that Bane is literally Lethality+Mercy. I will grant you that most of that is irrelevant against the three Mantle bosses, but it still leaves Volke a LOT more capable than Sothe/Heather against all the rest. Pretty impressive given the general tendency of non-royal late entries to suck.
Also, on the general strength of knives, Baselard sits at 18; the same as Alondite and Ragnell. You take a large power drop for a ranged assault with Peshkatz, this is true, but a Whisper dedicated to close combat could do quite well if their Strength caps weren't so horrible.
3. Sigrun is available in one chapter before part 4.
3-11 and 3-E. Check your sources.
Elincia also gets more versitality due to being able to use staves and gets Amiti in 2-F so she can hold on her own there. Oh and Tanith has better base stats than what Sigrun would have at a similiar level, is only 3 levels away and gets an awesome ability.
Bringing up Tanith only drives home my point, that Sigrun is an example of a character who sucks for reasons other than level/availability. She's as available as two other non-staff-wielding pegasus riders and amply leveled, but her stats simply do not measure up. So to claim that the entire cast is over-powered is wrong.
4. Mist starts out at level 1 when the other GMs start out at around level 8 on average
Mist also starts with Florete, a madly powerful and bizarrely light ranged sword, complete with high accuracy and critical. It plenty compensates for her initial weakness. The problem is, when your starting weapon strength is only 4 attack strength behind the SS weapons, it doesn't leave much room to grow. Mist does not have the growth rates to keep up, and even if she did, her Strength cap stops her entirely too early. Bonus EXP will only make her less of a disaster, but she can NEVER be overpowered (which is quite a shame considering what a beast she could be in PoR with a Sonic Sword).
5. True, but you must admit that the gap between Shinon and the other bow users was much smaller in PoR.
In ease of raising, yes. I don't think the performance advantage is that drastic, but using an alternative takes more effort. Then again, Rolf is at least competent to start with, he just doesn't get any lead time over Shinon like he used to.
Instead IS tried to be 'original' and went with an 'epic' story with a 'huge' twist that the dark god was actually part of the good guys and that the goddess you've been all worshipping was actually the bad one. No actually that there was no good or evil in this story, just something about order vs. chaos. Excuse me, but there's a reason why all the most popular fictions all are basically the same dozen or so stories retold and that they all revolve around good vs. evil, so why did IS feel the need to stray away from that, especially since that way they also destroyed everything that PoR established?
The better stories out there tend to challenge the absolute of good versus evil. Heck, even PoR did to some degree, as virtually the entire storyline centers around conquering racial tension. For that matter so does MMZ; from day one you're on the side of "Mavericks" fighting against the "hero" of human utopia. And throughout Z2 and Z3 Harpuia challenges his own beliefs.
Ashera is evil for the same reason that Copy X is: Apathy. She doesn't question herself and cares nothing for the people under her. The twist isn't the switcheroo from public perception, as their roles were quite reversed in ancient times when Yune was out of control (and incidentally PoR implies that the "pop" Ashera is invalid; see Stefan's support conversations with Mordecai). Rather, the twist is that Ashera and Yune are in fact the same person. In trying to "fix" herself by casting off what was unwanted, she started down a dark path and very nearly sealed the fate of all that she (previously) cared for.
I finished RD within 80 hours while I finished SD within 15.
Hmmmmmmm!
RD is unusually long even by FE standards, and SD is a handheld based on an NES game. Kinda opposite extremes, as far as FE is concerned. I said that both are adequate, not that they're comparable. Simply put, I don't see SD as too short. I do see it as incomplete, knowing that FE3 on the SFC offered a remake and more (that and even the uneducated know that there's more to the story if they've seen Marth's SSB trophies), but that's not the same thing, and the DS sequel is aimed to fix that anyway.
Then again you put characters on a higher priority than the overall plot so I suppose that's where our opinions differ.
Only because if the characters aren't involved in the plot, it makes the entire gameplay scenario feel unrelated and a lot less compelling. If you have no attachment to who you're playing as, you have less of a reason to keep playing.