Alex Ovechkin, recently crowned as the greatest goal scorer of all time by virtue of raw totals as well, got his NHL career started in 2005. We know he's been incredibly consistent and durable, almost scoring 50 in three different decades (paced for over 50 this season). The raw peak of 65 goals is good but not incredible. Then again, it's still estimated as the 2nd best OAT in adjusted goals (after Brett Hull, if my memory serves). Most people would likely agree Gretzky reached his peak of 92 and 87 (pace of 94) goals in pretty much optimal conditions and wouldn't gotten so high once goaltending and defensive schemes markedly improved. Maybe the same can be said of other snipers whose MO was slapshot. Mario Lemieux, probably the most talented and versatile goal scorer, stayed effective heading to the dead puck era and even torched the league in one of his comebacks in 2000-01, though the sample size wasn't ample. Pavel Bure seemed quite unphased by changes in league wide scoring but wasn't built for a long career. Brett Hull might've had the best peak but how much of it do we credit Adam Oates for, and how would that short-lived companionship have played out during the post lockout salary cap era? Do we even care to think of the early forefathers, the likes of Frank Nighbor and Joe Malone? This kind of thought excercise may raise more questions than answers but it's always fun to speculate.
For the purposes of this excercise I think it's fair to allow players reasonable health improvement, at least for the fact that they'd be able to enjoy the fruits of 2000s medicine including improved surgery techniques and rehab, changes in playing styles, rules (no red line, no clutch and grab), lifestyle (no-one smokes anymore etc.), advances in equipment and goaltending etc. Not sure about the effect of salary cap (unlikely Bossy gets to play with Trottier et al. his whole career).
I suspect Mario would be, perhaps rather narrowly but still clearly more prolific than Ovechkin in this scenario. Howe in 2000s environment might have even better longevity than Ovi and with a prime almost as good as Lemieux. Ovi might take third place. Bure would be close but he loses in longevity. Bobby Hull would be up there, maybe better than Brett whose peak was short. Not sure with Esposito here, does Orr play in the 2000s as well, lol. Bossy is a curious case as a great candidate for the oft-quoted demand for 20x45 goals (to get to 895). No idea with Rocket Richard. I think one clear loser here is Matthews who doesn't get any advantage of what if - if anything, his numbers would drop. Of other notables I'd see an increase in Teemu Selänne's numbers even though he'd be hard pressed to reach his career high of 76 goals. As for The Great One I don't know how to place him but I don't think he makes the top3 and it's unlikely he gets the single season record either, looking at how he used to get his goals in the 80s -- then again you're reminded how much better he was than everyone, including Bossy... But given how much more talent there's today I think he really goes wild as the best playmaker.
Gretzky would still take off in early years and probably be #1, or close....but eventually he slows down and gets surpassed (as his goal-scoring career played out in reality).
Ovechkin has excellents odds to be #1 by 2025, 20 years later. In fact, he's definitely the favorite to me. Gretzky wouldn't keep up over the long-term, by year ~15 Ovi would pass him. Here are the few names who might keep up:
1. Mario Lemieux. He's a better goal-scorer than Ovechkin (or anyone else). Give him perfect health & longevity, and he's #1 all-time, and by a lot. I think OP is implying some reasonable health improvement - but it's hard to figure out exactly what that means. If he plays enough healthy seasons, he's #1
2. Bobby Hull. Tremendous goal-scorer. He doesn't really contend for most raw goals ever for two big reasons. First, his era was very low scoring. Second, he left for the WHA. In this hypothetical - neither dynamic is in play, so I think he would be Ovechkin's biggest threat. I still see Ovechkin finshing ahead though - it might be close through age ~35 or so, but Ovechkin simply hasn't slowed, and I think he would win the marathon of a race
3. Mike Bossy. If you ask me who the most consistent goal-scorer of all-time in their prime was, I'm tempted to have Bossy #1, or close. Up until he retired early. So - his whole 30s is a huge question mark. Is he the type to age well with good health? It's possible. My guess is he stays close to Bobby Hull and Ovechkin for a while, but I think he slows down a lot by age ~33-35 and doesn't keep up long-term. But - it's just a guess, since we didn't see him age out.
4. Auston Matthews. Tremendous goal-scorer. Injuries have hurt him quite a bit too...no major injuries, but just nagging ones that have definitely impeded his goals in some years. If you improve that for him a bit health-wise, I think through age 27 (his current age) he'd be ahead of Ovechkin in goals. Obviously the huge question mark is how long does he keep it up, and how well does he age? One more issue - I don't know that I see Matthews as the type of person who wants to be playing up to age ~40. I could see him retire early, rich and enjoy life by age ~35-36, and if so he won't contend for raw goals. But - if he did play a full career, he'd be a contender.
I don't think anyone else challenges Ovechkin. Both Maurice Richard and Gordie Howe would score a ton of goals and rank very high (possibly even top 3-5), but Ovechkin remains ahead.
So - for me it's Ovechkin #1 for raw goals, with Lemieux being the only one who can top him, but it all comes down to health.