Soloing didn't destroy this game. I did it back when we still had to grind for stuff (during the abhorrent first epic system when everything was CC and DPS against all immunity high HP critters). What changes was that instead of finding a middle ground between grinding for items with silly random criteria (like finding THAT epic shard or seal) we instead got the trad-able named EN, EH and EE without needing to actually run anything.
And perhaps the worst part was to release a lackluster xpack that completely destroyed the value of named items. EGH was a good thing. It added some additional life to the game and was swiftly destroyed by Shadowfell.
Worst of all? Why even run Shadowfell? I mean other then for favor and some XP? The named items are terrible, random items OP and there's nothing else to grind for. MOTU had at least a destiny grind (terrible as it is) and a raid item grind. Even a upgrade system of getting comms, enough favor and unlocking set bonuses.
The current xpack has nothing.
MMOs need hamster wheels. But hamster wheels with nice pictures of open landscapes in front of them. To fool us into believing that we're not actually in a hamster wheel. Kind of like Greensteel mat and item grinding. We always saw a forward goal. We always got something out of it, a milestone towards our goals.
We need a better idea of milestones again where we always get incremental steps towards something and when we get there we also have something we need that stuff for.
Back when we hit 20 it was almost a gold standard to need greensteel to get ToD rings and these to better deal with Epic items. The slow grind of Epic items help us master Epic quests.
But ever since MOTU and beyond we have always had an almost instant gratification to overcome every single obstacle and now it's almost pointless to even try to get better stuff since it will have an marginal impact on our ability to group smack anything we face.
What I think we need is to stop increasing the level cap. To have something (a long term goal with incremental steps towards) to grind for while creating a system that challenges us.
There's plenty of content in DDO right now for people who want to hit things at whatever slow pace they like and plenty of ways to get instantly gratified with power items.
But there's virtually no way for true challenge or even longterm goals.