If Ovechkin retired today, he would absolutely be in the conversation for greatest goal-scorer in NHL history.
Prime - this is probably the strongest part of his case. He placed in the top three in goal-scoring 12 times in 15 seasons (in a 30 team league) - that's nearly unfathomable. Assuming the 2020 season ends here, he has nine goal-scoring crowns in 13 years. The only player who seriously rivals that is Howe (first or second in goal-scoring ten times in 14 years - and of course this was in a smaller league with less of a chance for another player to have a big season).
Career - another major strength. He scored 700 goals already, in a low-scoring era. He has a realistic chance of reaching 800 goals. He already ranks 5th all-time in terms of his era-adjusted career total (based on VsX) and he's around two seasons away from second place. I doubt he catches Howe, but this is another strength in his case.
Peak - eight (nine?) Richard trophies is very impressive, but most of the wins were by relatively small margins (five of them were margins of five goals or fewer). His 2008 season was a historically good season (on par with Gretzky's 92 goal season taking era into account), but none of his other seasons stand out to the same degree. Compare this to, say, Bobby Hull, who dominated the league by huge margins multiple times. Obviously the league is different now, but aside from 2008, Ovechkin's margins of victories aren't much bigger than his peers (Iginla and Stamkos both won goal-scoring titles by 20% margins, which is comparable to Ovechkin's best outside of 2008).
Playoffs - his per-game goal-scoring rate drops about 16% in the postseason - slightly higher than the overall drop in playoff scoring. He only made it out of the second round once (but did very well in the last two rounds of 2018 - seven goals in 12 games). That stretch where he had only 26 goals in 69 playoff games definitely hurts. I wouldn't go as far as calling his playoff goal-scoring a weakness - his Smythe run silenced many critics - but in general, the postseason isn't a strength like it is for other players who have a claim to this title (especially Gretzky and Richard).
Intangibles - there are two main arguments against Ovechkin. The first is that he's predictable. I disagree with this one. I mean, it's literally true in the sense that Ovechkin's goals are less varied (and less aesthetically pleasing) than, say, Lemieux's goals. But we shouldn't be evaluating players based on their YouTube highlights - productivity is what ultimately matters. If Ovechkin truly was predictable, why would he keep winning goal-scoring crowns, year after year?
The other argument is Ovechkin is one-dimensional (in the sense that he has a singular focus on goal-scoring - forget playmaking). There's clearly some truth to this, after his peak ended. (From 2012 onwards, of the top 200 scorers, he has the 2nd lowest assist-to-goal ratio). If we're strictly talking about goal scoring, then this shouldn't matter. He scored the goals he scored, and that's that. But I think it's worth asking if goal-scoring titles with 38, 38, 28, 28, and 21 assists are nearly as impressive as, say, Howe "only" finished 2nd in goals one year, while leading the league in assists. How many more goal-scoring titles would Gretzky, Howe and Lemieux have, if they shot the puck a bit more?
Taking all these factors - yes, there's absolutely an argument for Ovechkin being the greatest goal-scorer in NHL history. But he's one of several players (Richard, Howe, Hull, Gretzky, Lemieux) who can make that claim.