Even with 1.05 changes to made default combat speed 2.0, several premade sovereigns have it still at set 1.0. Also, it happen to all 3 heroes from campaign too.
There are other non-hero units that have this too. Like Sentinel from Warlord trait, or those Fallen pre-designed peasants.
I looked a bit into various xml files, and I think the issue is that all these unit had no combat speed attribute set at all, so game defaults it to 1.0.
