So then why are you badmouthing cards that just don't fit in the current meta?
To support my argument that grow effects were historically weak, which is why Undertaker seems pushed compared to his colleagues.
It's not a matter of "Undertaker is overpowered because its power distribution isn't in line with these other similar cards" but "Undertaker is overpowered because they realized this kind of card needs to be overpowered to be worth playing at all".
Actually, I misread your post, but I still disagree. I am not evaluating these cards based on how they perform in this meta, but in every meta I remember since I started playing.
Mana Wyrm: Playable when Freeze Mage was dominant. I chalk this up to the power level of Freeze Mage before the big nerf, and the undeveloped understanding of the game the community had at the time. Mana Wyrm looked like a good card, and it had nut openers with Arcane Missiles, Mirror Image and Coin. But modern Freeze Mage knows that Arcane Missiles/Mirror Image are actually not great choices, and Mana Wyrm was sidelined along with them. Playable in Aggro Mage, which was competitive for maybe two months in Spring? And only on the ladder.
Frothing Berserker: Played in early aggro Warrior decks and early Control Warrior shells. Aggro Warrior was always kind of lacking, and Control Warrior was underdeveloped as an archetype because people just didn't have access to all the cards it really needed to reach its full potential. Notice how, despite the addition of Death Bite and Unstable Ghoul, both cards which are played in current Control Warrior decks, and both cards which synergize with Frothing Berserker, he still doesn't appear in the "complete" Control Warrior lists. It's just not a good Control card, so it's inclusion in historical Control lists can be considered an accident.
Unbound Elemental: A common 3 drop in early incarnations of Midrange Shaman, which, really, is the only Shaman that ever existed. Despite most Shaman decks these days running a suite of Overload cards, (Lightning Bolt, Feral Spirit, Lightning Storm, Doomhammer, Lava Burst, Al'Akir), this card no longer sees play. What replaced it from Naxx? One or two Undertakers. Two Spectral Spiders. The thing that was really holding Shaman back then was Hunter's Buzzard/UTH combo, and now that that's gone, and Shaman is a real class, Unbound Elemental still hasn't made a resurgence. That tells me it was never really good, just filler because there was nothing else worth playing. As soon as a better card came along, Shaman dropped it like it was hot, despite having really good stats for its cost.
Starving Hyena: This was playable in UTH/Buzzard's heydey, but it was never overwhelming. It was a removal magnet, and unless you played it on the same turn of your UTH/Buzzard combo, it died instantly. Often, it would die even if you managed to grow it. But it worked because UTH/Buzzard worked. When they killed UTH/Buzzard, Hyena went with it. Or it was cut for Undertaker/Spectral Spider, just like in Shaman decks.
What's the common thread among all these cards?
If they were played, it was because the class they were in had some overpowered mechanic to carry them (classic Freeze Mage, old UTH/Buzzard), or if their deck design was underdeveloped (Control Warrior, Midrange Shaman). As soon as the nerfbat hit key elements in their respective classes, or if better choices for the same decks came along, they faded out.
