Hmm... I don't think the devs changed how pack units work. Maybe they tweak the multipliers a bit, but during my low-level run, I didn't feel having high pack unit really boosted my alpha unit's stats.
But then again, I haven't really tried doing this when using special goblins as pack units. Since I easily sacrifice them to the altar to avoid reaching the cave's goblin limit.
Yeah, if you have a decently built army, 5-star Difficulty isn't that hard to beat. Unless the devs release another boss like Nefarious in this game, then maybe things might become a little bit challenging. As for defense battles, I have a paladin with 1k+ Defense, so mobs aren't able to scratch it at all... As for heroine defense battles, then I usually use traps that reduces the enemy's range, put up 2 of them, and heroines at the back row will become useless. In my first playthrough, I also use either SP recovery traps, or SP reducing traps depending on the heroine I battle. Right now, range-reducing traps will render possibly magic-dealing heroines(Nobunaga) useless.
Null active skill, huh? In the early game, I usually use those heroines for the main goblin line I have to keep it clean from skills. I used Hanzou for attack, Magoichi or Ranmaru for defense. However, as soon as I got Mitsuhide's skill, I stopped caring about keeping my main goblin's line clean. I keep breeding my goblins with Musashi as she had 4-stars in attack. Goblins breed with Musashi, and Hanzou has too much of a gap later on, so I went with Musashi. For defense, I only used Magoichi/Ranmaru since Invasion-Type Nobunaga was bugged in my version before. But Invasion-Type Nobunaga has the highest growth rate for defense.
It's a bit of a hassle, but doing this will make your pack units super buffed later on. If I want a certain skill for my alpha unit, I'll have to do it the hard way. Breed them with a heroine with a skill you want, then clean them using heroines without a skill. I only update my alpha unit once a playthrough though, so it's actually not that bad.