4th Gen Level curve of heartgold/soulsilver

So i just reached lance with a severely underleveled team at level 37-40, my team is fairly balanced with feraligtr, heracross, crobat, ampharos, gyarados and nidoking.
Both gyarados and feraligator know ice fang but lance's dragonites are insanely high in level and it would take me hours if not days to grind to an equal lvl as him when wild pokemon are at most level 30.
I've played almost all main series pokemon games but never finished a jhoto game ever, is the curve really that bad or do i just suck?
The closest i ever got to beat him was when i only had my feraligtr left against his charizard but he got a critical hit with air slash so that kinda sucked lol

The last 2 times I've tried to replay HGSS I've given up around the 5th gym because every time I realise my team is way underleveled, and I also realise how tedious the grind is in those games and decide I can't be bothered.

The leveling curve in the Johto games is ass so it's not you.

It's possible to beat the Elite 4+Lance without your party being roughly the same level. 40 is the minimum that I usually aim for, and I really I don't go in at a much higher level, if at all, because, y'know.

Never had a problem with Johto I tend to get my pokemon levels up so I'm always higher than the gyms or elite 4, I tend to battle every person and pokemon I come across

I had the same level curve problem. with my last playthrough, when it comes to the trainers before Olivine, my pokemon are already some levels behind. I remember I had to grind (which I didn't like since the ds games are sooo slow)

The leveling curve is certainly one of those things that grated on my nerves when I played the Gen II games, and even the Gen IV remakes didn't exactly address the problem from my viewpoint. Leveling up consistently in the Jouto games is a chore, and I feel that Game Freak didn't properly test the games, otherwise they would've noticed that problem and fixed it.

Johto: a region where you can find wild Pokemon below Lv. 20 just before the 7th gym.

Johto had the worst level curve, honestly. They fixed it a tiny bit in the remakes, but, it's still horrible, so no, it's not just you.
Although, I guess the same can really be argued about the third generation before it...it definitely doesn't help that the Pokemon in Victory Road aren't that high leveled either.

You know, when I first played gen II on release I don't think I noticed the level curve being so steep. Maybe I just had a higher capacity for grinding mindlessly as a kid. I definitely remember losing to the Elite Four/Lance a lot though - I think I usually just spent the majority of my money on revives and potions so losing didn't matter that much, and I would level faster gaining xp from losing to the Elite Four rather than grinding low level wild pokemon endlessly.