Ovechkin, Malkin, McDavid, Kucherov, Thornton. Sure a couple of them might be debatable, but I mean so are Draisaitl, Kane, Hedman, Karlsson and a couple of goalies aswell, point remains if he is not even clear top 5 for peak of players currently playing it's ridiculous to claim he is 5th best of all time.
Crosby's peak level of play is as good or better than any of those.
Full peak regular seasons? That's a bit more hit and miss, since injuries kept him from full seasons in that ~2011-2013 timeframe. I'd still have him ahead of Thornton for sure, as well as everyone in your 2nd group.
Definitely ahead of McDavid too - McDavid's best full season is 2017-2018, Crosby has a few better ones. Fully acknowledge that may change in McDavid's favor though in future.
As to the bolded - no it's not ridiculous. Crosby's strength isn't his full peak seasons, but his prime/consistency. His playoff/international pedigree doesn't hurt either. He just broke the record for most consecutive seasons over a ppg (beating Gretzky) with 16. Considering the lower scoring era he plays in, that's commendable and truly staggering in terms of consistency elite play. Howe, Bourque and maybe Gretzky are the only players all-time with arguably a more consistent high end prime than him. That's his calling card imo.
Also - you were talking a few posts up of Harvey, and Lidstrom. Harvey's peak doesn't surpass many of the players he played around the same time as - and Lidstrom is even worst, as he's quite weak for peak. Bourque is in that ballpark too - his peak is nowhere near as high as Lemieux, Hasek, Gretzky, Yzerman, Jagr and I can keep going - he still has a fine argument to be in that vicinity of 5th spot.
Different paths to greatness. Crosby's path excludes the highest of "full peak regular season" - but he still reaches that overall level