Dark Rising only ever boosted legendary stats on the E4, where, in addition to being comically over-leveled like everything else in the hack, you had to deal with 800+ BST legendaries stuck in the middle of full teams- the champ then proceeded to use all of the E4's aces alongside a 1010 BST Lugia with 200 BP Dark STAB. It wasn't really approachable without gratuitous amounts of item spamming cheese or surgical over-preparation as your pokemon were fairly vanilla. That said, talking about Dark Rising's use of...pretty much anything...is a rather boring subject as most of the time the answer is "it sucked".
Ah, thanks for clarifying. So we're talking sharp level curves to create fake difficulty that can only be combated through level grinding or cheating. In that case, yeah, I don't like them. To the point where I don't think they should be included even as difficulty patches, because that's not how you create difficulty and make a game fun. Good game design allows for difficult play without tons upon tons of grinding, and to be truthful, I think any hack that requires grinding without an efficient way to gain experience has succumbed to bad game design, because all it grinding does is bore the player.
With regard to the more interesting topic of high-stat single-enemy bosses in general: Difficulty can come from many sources, but Pokemon's mechanics work best when the enemies are on the same playing field as the player. Bosses are generally many normal enemy Pokemon against the player's many normal Pokemon- breaking the mold with a singular inflated boss enemy requires careful handling as you either get a comical anti-climax (see BW2's Kyurem battle) or an uninteresting, demoralizing clean wipe if you didn't prepare (see a certain hack's level 70 Kyurem encounter prior to the 4th badge). I don't think making a superboss be fair is impossible, but making it a serious threat to a prepared player while still being interesting and fair against someone with six all-out attackers is unlikely. There's far too many ways to cheese a single enemy in Pokemon, such that taking all the options away would make the game much less interesting- type advantage, Toxic, Paralysis, Destiny Bond, OHKOs, Curse, Perish Song, Leech Seed, Charm/Light Screen, Sand Attack+Recover, Spite, Disable, Encore, Hyper Potion/Revive spam, timely crits/brightpowder/misc. hax...the list goes on. There's also very little reason to switch when there's only one foe, which simplifies things even more.
Yeah, there'd have to be a lot of changing to be done. Not just on a stat level, you'd have to restrict the possible moveset and make it so that the boss is self sufficient, to the point that they can take care of themselves without being complete sweepers. And that's kind of the problem. With my hack I'm using a party of individuals gathered throughout the story, so it's not a particularly difficult issue because the types the player has in their disposal and the moves they might have will be fresh in my mind, so I can design the bosses (and the available moves) around that framework.
But with Pokemon, you're right, it's not so simple. And I really think a large part of that stems from the fact that Pokemon is a game where the enemies' Pokemon can be just as strong as the players' (because, in a sense, every pokemon has the potential to be your pokemon). This is why the "mob" enemies exist as wild pokemon, and those pokemon are only weaker due to lack of EVs, lower levels, intentionally lackluster movesets, and the simple AI. Because Pokemon is a game where every pokemon is meant to be caught, and the challenge and difficulty of the games, because of the number of options, is more in the hands of the player than it is the developers (depending on various things).
But I really do wonder if creating a character/Pokemon with high HP/Def/SP Def could make for a real challenge. This is what I had in mind, but I do have my doubts. My hack is very boss-based and, other than my own, I'm a big fan of Pokemon hacks that feature boss battles (which are few, for reasons we've been over) because they allow for a plethora of new avenues in storytelling to be explored. I mean, I would assume that, should the boss be self sufficient in ways where status problems wouldn't be fatal, but could still deal damage (unless that specific boss is immune), somehow maintain his accuracy, possibly be immune to OHKO/Suicidal attacks, and not just not be completely borked by 1-2 takedown strategies, then it could make for a challenging boss, but looking at the list of things that can bork the bosses really makes making a boss seem like a challenge in itself.
...Actually, on that point, would it be possible to implement hidden abilities into Gen 3? Because if it were possible to create a hidden/second ability that had several functions, that might eliminate a few brick walls involved with creating a boss worth a darn..