We probably shouldn't judge performance by the way the game runs in the 1936 |1937 footage but rather performance in 1944 | 45 (which we haven't seen yet) because there's going to be a bunch more units and models on the map in 1944 | 1945, and consequently more calculations for AI, supply, etc. etc. So even though I have not seen the game perform poorly, it might be that the game has performance issues I haven't seen, and so I believe them if they say the beta build was not performing as well as they need it to.
And in terms of whether the game is officially in beta yet, just remember that during the same time period we're talking about paradox making these beta submissions (November & December 2015) they also moved offices, released a major DLC for EU4, and of course the holidays. Also there was apparently a round of illnesses in the office too, some people missed the developer multiplayer sessions due to illness.
Whatever the reasons might be, It doesn't really worry me that the game has not had a successful beta submission. why am I not worried? Because I really believe in the dev team. I have watched the interviews with them and seen the footage available, seen the dev diaries and searched and read the developers forums posts like a sneaky little troll and basically what I've found out is that these developers are
a) quite clever
b) big HOI fans
c) aware of and insightful about the problems in the previous games in the HOI series
d) not being forced through the development cycle to meet an arbitrary sales driven release date
All of the above make me feel pretty good about the game. Also, if you haven't searched the forum to read posts by the Devs, you really should. Some of those posts are fall down laughing funny.