Leftists should be doing combat training if they have the knack but I don't think it is as important to a socialist revolution as it is to a fascist one.
Fascists use intimidation and violence to enforce their ideology. They exclude and persecute minorities but they are sure to communicate that if an individual isn't supportive they can be targeted too. The only way to prove yourself a good fascist is to do inhuman acts to minorities or anti-fascists. Violence is the only path of upward mobility for most fascists.
Leftists use community and organization to build government after the masses overthrow the capitalists. The left does need people that are capable of violence but the primary concern is agitation. Why do martial arts training for an hour if you can make a crowd of ten people angry at capitalists instead?
Tactics is definitely something that leftists should study. If you can agitate and direct people to victory they will respect you and that respect can turn into support for the party easily. (I should read more Mao.)
There is a lot of brainwashing that goes on in German schools so if a quarter of 18-24 year olds are voting for "don't send weapons but israel has a right to defend itself" that should be taken as a good sign.
The east is a podcast has a really good 2 part interview about zionism in germany.