Up to date as of 12 November 2022 (update "Fire and Ice")
Main points (TLDR)
Less grind due to max. 2 vehicles per rank, per branch
More branches to choose from give more freedom, you can skip some branches and still unlock next rank
Branches are consistend gameplay and/or historically wise
Vehicles up to 1945 in ranks I-IV, post war vehicles in ranks V-VII, and lines are not connected due to differences in design philosophy as well as time gap.
Current state in game
German ground tech tree is probably the one which has the biggest gap between how badly organised it is in the game currently, and how good it could be. The worst offenders are the left and right most branches. Left one starts off as light destroyer branch, but it has the puma randomly in the middle, and then without any connection break it goes full light tank. Right one on the other hand starts off with Pz.35/38t's, and then goes full destroyer, yet for some reason it also contains DF105 and JaPz.K A2 light tanks in the middle. I don't even have to mention that Gaijin fully abandoned any attempts to make tech trees that make any kind of historical sense, or at least have gameplay consistency. Also, Wiesel 1A4 is classified as SPAA, for reasons which are beyond me.
Most branches are organised with gameplay consistency in mind. There are some exceptions from this:
The wheeled WW2 line is a mix of destroyers and light tanks, but I think that wheeled flavour makes up for it. Also, without it, there is nowhere else to put the Puma.
The KanonenJPz and the RaketenJPz are put together since they use the same chassis, and also they dont really fit anywhere else.
In the post-war section, MBT's and LT's are split according to them being either an import / export / international collaboration vehicle, or a native development. This gives us two neat lines of each.
Despite the lower BR, PUMA is above the RadKpfw 90 due to their age: they are from 2009 and 1986 respectively
Then, there is the big split: all WW2 and earlier vehicles are in ranks IV and below, while the post-war vehicles are in ranks V and above. The two sections are not connected by the arrows, so the player who reaches rank V can begin research of any branch there, regardless of which branches he unclocked before! There are two good reasons for this. First, historical one. There are 10-15 year gap in the german development of armoured vehicles following the end of WW2, which causes huge jump in design philosophy of the vehicles. Second, gameplay reason is the result of the first one. The vehicles play completely differently! While up until the end of rank IV we continue to get thicker armour and bigger guns, next rank shifts greatly from this, instead having lightly armoured, mobile machines filled with new technology, such as night vision, stabilizers, ATGMs etc.