I know they lost a ton of the best characters - but the formula of a clear build towards Thanos was amazing....how did they lose sight of that? This is an uninteresting mess.
I don't think they lost site of it at all. They are using almost the identical formula they used for Thanos as they are for Kang.
The two big differences is they are trying to shoe horn in multiple tv shows into the arc, and most importantly, very few people are enjoying the Kang multiverse story line. The story line is at best confusing and at worst boring and uninteresting as you suggested.
I may be in the top 1% of Marvel fans (in terms of not being too critical) but this Kang arc does not have me looking forward to the two Kang Dynasty movies at all.