Somewhere betwixt the two would be nice. Early 40k was basically just early GWS guys begging, borrowing or stealing any idea they thought was cool at the time to build their universe. (Everything from Dune to Micheal Moorcock.) Which is why you got beer-drinking, seks-having demigods with AK47s for Space Marines. It took the universe a little while to mature its ideas, to achieve some narrative consistency, build its lore, yadda yadda....Today, there is just a teetering mountain of facts, ideas and histories to the IP that if often doesn't need to steal, or innovate, because it just keeps doing what it's been doing for decades now. And that gets a little boring.
I'm of two minds of space marines. On the one is that, yeah, early space marines were more believable in their space marine-ness. They were more flexible, the ideas more capable of surprising you. The other though, is that current space marine fiction allows them to have a concrete identity, crafted and shaped by themes that go beyond the color of the livery and the flavor of their mutations. Chapter histories can go deep because someone took the time to apply rigor to the ideas. I sometimes wonder if the seeds for the Heresy were planted in 40k by the idea of space marines unbound by anything.
At the end of the day, having read a decent amount of Rogue Trader and early 40k fiction.....I find I prefer where they ended more than where they started. While believably flawed (read as: human) space marines does make for better variety than we have now, it came with its own silliness and incongruities. The discipline that comes to define space marine ideology needed to be practiced at the conceptual level, too.
Otherwise we'd potentially have the Hello Kitty Chapter as canon, in some form. Pink glasses and what not.