I love (and am endgame in) both. I come back to each, check out the new stuff and drop it when I've done enough. Elite is IMO the grindier of the two, once you're through the initial BS in NMS it's just muck around and have fun, in Elite that takes a looong time (way less now, I was there in the first days, dear goddess), like carrier and 10B, before the FOMO goes away forever and you're just mucking around. These days I mostly go back to Elite for CGs and when new stuff can be bought in game and often do NMS expeditions.

To OP:

Both are fun and good value, but the miles wide and inches deep thing is true. Elite has basically no story / quest (plenty of backstory though and a background simulator) and dumps you in the deep end. NMS does have a fair few hours of quests which helps you get up to speed, but it's mostly optional (some unlocks in there). In both you have to have enough self direction to make your own adventure, but sounds like you've got the explorer spirit, likely a good fit, for slow too.

If you get into them they're some of the best values around, super easy to sink hundreds (or more, sigh) of hours. If you like arcadey low stakes fun most, go NMS, if you want a 'real' feeling of space, better combat, killer sound, can cope with some grind, and are OK with meeting the consequences of your actions (don't fly without rebuy kids) Elite is the way. Either way, if you get into one, the other is likely worth checking out eventually.

I love Elite and it's definitely amazing in VR. For everything in a ship I agree with you, NMS is childish in comparison.

However, NMS is attempting a way more multi-cultural galaxy, and I often wish Elite had more diversity in aliens, and more interesting planets similar to NMS. Especially when Elite has so much grind to do rep etc. I wish just once I'd be doing a delivery quest to an acid jungle planet covered in hostile turtles, instead of yet another dead planetoid with a few outposts sticking out of it.