Whilst I personally prefer Captain these days to regular Toad; I'm afraid I don't agree at all with that comparison.
Yes they both require rescuing at some point, but Toad takes on a far more active role; even at his most NPC, Toad is usually depicted aiding Mario in some sort of way opposed to the animal friends who...don't actually aid Sonic in any way. When was the last time Johnny Lightfoot aided Sonic outside the comics for example?
Sonic animal friends and Chao have also
never been playable characters unlike Toad. Cheese the Chao is arguably playable in one game and in as much as Luma is playable in Smash since you technically play Cream and send him to assault everything on stage. You don't really play as Cheese.
To put it lightly;
If Mario is Player 1 and Luigi is Player 2 then Toad is Player 3. Or 4. Or sometimes both game depending. Whilst NSMB required all four characters to play the same(for some reason; guess they threw that idea out in Luigi U with Nabbit) Toad has still been playable in SMB2 and 3D World platformer wise.
Also worth noting Mario and Luigi play identical in the NSMB games despite the fact we're well aware Luigi has lower traction, a higher jump and overall tweaked stats to Mario in many other games.
Likewise Toad is usually depicted as; more powerful than Mario and Luigi(seen via Turnip Pluck speed in SMB2 and various references to 'surprising strength'), faster than the brothers(and Peach) and with crappier jumps. Even regular Toad is at least as unique as Luigi is to Mario at this point. How unique that
actually is comes down to personal opinion.
Not that I'd be against deleting Doc from Smash entirely and having Toad as a Mario/Luigi Semi-clone with a few tweaked specials(like giant turnip pluck from Peach). He'd have a little more merit than Mario in a labcoat at least.
You mean the game where Wario doesn't do anything at all apart from appear at the end as a boss? Yeah, I doubt anyone can take Wario's Woods away from Toad. That was HIS game, no question.
But hey; I'd be down with a Wario's Woods inspired moveset too; running up walls, summoning and stacking enemies to use as projectiles and use them as cover from attacks, line up three monsters, set off a bomb and create a massive explosion. That actually does sound pretty cool as a gimmick to me for regular Toad.
Alternatively; Toad is also able to summon mushrooms in Mario Sports Mix, which is another power that is unique to him:
In fact overall Toad is probably the Mario character MOST associated with mushrooms. Apart from his obvious appearance, Toad's special item in Double Dash(the only Mario Kart to have unique weapons) was the Golden Mushroom, which is something Smash Bros. Crusade ran with, and not to mention the very often overlooked ability to create spores.
Toad originally showcased his spores in Mario Tennis 64 befpre becoming a Smash staple. Should he have been included it's a safe bet these spores would of been in his moveset too.
Considering the amount of Toad Houses he's run as well, the minigames from the NSMB series Toad Houses are also unique moveset fodder for the more generic Toad.
It's not like Toad has NO unique moveset potential. It's just considerably less obvious than Captain Toad's moveset potential...
...which is why I have to agree with this statement as well.
Additionally as much as I'd be up for a default Toad alt(I'd freaking love it, that Toad was my childhood after all), considering his moveset will most likely include the backpack; a major gameplay excuse of the Captain Toad game, and his headlamp I can't see how regular Toad would be able to even be an alt...at least without those two pieces of clothing.