By original design, this game was intended to be group centric. It's not my opinion. It simply is the way that it is.
I don't know where you get that idea, because UO was never designed in any way to be group-centric.
In fact, it wasn't until the addition of Champ spawns that anyone at OSI/EA ever even made mention of needing to group with others to fight something.
When EQ moved to top position in the MORPG world, the single largest complaint by players was Always the same one, that they HAD to group to accomplish goals that Every character would eventually have, regardless of how one actually wished to play the game.
Many of those unhappy players returned to UO.
Each successive new game that has effected UO's population has had that same issue. They all require you to depend on others to accomplish YOUR goals, and that keeps people turning back again and again to UO.
Look around in the game for a while.. Look where people are and what they're doing. Look at what is actually Being killed, and what sits unused.
The more people it typically takes to beat something, the less you see even bothering.
If requiring more players to beat something were actually somehow a BETTER way of doing things, why do you think the peerless that require the most to beat are also the least often visited?
How many visits do you think Paroxy gets a day compared to lady Mel? 2 vs 30 maybe? Because PoP "Typically" takes a full group at the minimum while lady mel can be taken by just a bard/mage and a full mage with relative ease if they are willing to invest the time.
It isn't rocket science after all.
If you sell socks and 90% of your customers buy blue socks, and only 5% buy red ones, you don't keep cranking out new styles in Red, you make them in Blue.