Im not quite sure if you are supposed to move your moonbeam (for example) when you are bear or not tho.

The
5e rules say you can, or at least I don’t see why moving moonbeam should be different from calling down lightning which is the specific example given:
Transforming doesn't break your concentration on a spell you've already cast, however, or prevent you from taking actions that are part of a spell, such as Call Lightning, that you've already cast.
Bcs once you have single form that is superior in every way, there is basicaly no reason to have any other.

How many moon druids that had acess to Polar Bear used Deep Rothé?
As you say, as a player it’s about picking the right form for the job, and as a developer making sure there’s a use case for each form, ideally throughout the game but at least at certain levels and that we can get good use from each form before getting something better. Level 6 feels the right time for a new fighting form as I find the existing beast forms are starting to struggle in combat by level 5, and a form with some decent CC like the planned owlbear feels a useful step. Though as you say hopefully it won’t make all the other forms obsolete. I’m cautiously hopeful, as I don’t think Larian have made that mistake yet.
Currently, as a moon druid Polar Bear is useful for tanking when the Druid’s AC and HP are at their lowest at levels 2/3, but I found wolf better at levels 4/5 for DPS once its Pack Tactics (eg with Flaming Sphere) were used. Dire Raven as you say is great for mobility, even without proper flying (which would be great), and cat is useful for sneaking, and both will be more convenient once the encumbrance issue is fixed (Larian support did confirm to me that it would be). Deep Rothé is good for breaking down walls, and also in fights with lots of verticality where it can charge around knocking enemies over (ie it’s handy in Grymforge). I didn’t use spider or badger as much in my run, but they both have situational uses, and I can imagine using them more as a land druid.
That is, so far, so good, and as long as Larian continue to consider ways to keep at least some other forms relevant, out of combat if not in, playing shapeshifting Druids should be as fun and versatile as it should be. As long as those concentration spells and other issues with spells (eg Sleet Storm not working properly on different levels and too-easy-escape from Druid’s AoE CC spells by jumping) are fixed, that is.