I dunno, I'm struggling to think of any recent Hot Toys figure (in say the last 1-2 years) that was significantly worse in the final production version. I think they've got their process down to a pretty fine art.
Plus for this particular figure I will no doubt have him with helmet on most of the time anyway. But that's personal preference. Understand non-helmeted sculpt should still be excellent.
I also think vendors are reducing the number of excess numbers they order over the pre-ordered amount to reduce risk of sitting stock. (Thank market saturation and over orders for Star Wars TFA figures for this - generalisation I know, but these are the factors I see). Sure it depends on the figure and film of course. But I've seen people miss the boat on a couple of figures where the after-market prices are crazy. Just look at Captain America Civil War, Dr Strange, Iron Man Mk46, Rogue One figures. Any of the figures with a classic look (or ones like Rogue One which will never be seen again) seem to be selling out fast, and have crazy after market prices.
I think this Loki could potentially be the last Loki (fan speculation aside), plus I'd say he's not the most popular of all the characters for most people. Therefore possible that vendors won't order too many excess.
Anyway, that's just my rationale to pre-order him now.
Roll the dice with missing pre-order, see how he turns out. Whatever, but I'll be happy to have this guy in the collection in the classic green with the classic horned helmet. My plan is to have him positioned in the lineup between Thanos and the core Avenger team. Should look awesome I think.