VW, Mercedes and BMW all use a modular basis and they can ,just like vw or tesla, place their battery on the bottom of the car without a lot of re-engineering. The only thing the classic manufacturers are actually behind in is production capacity for batteries, but that`s what they have join-ventures with samsung and co for.
So again, no, you`re grossly underestimating the classic premium brands.
All that`s been missing for the classic manufacturers to jump on the ev bandwagon is the will to abandon their moneyprinting diesel engines. It´s not like they couldn`t have, they didn`t want to....until china started to really force them and Tesla reached a certain size.
What I really don`t understand though is why bmw, audi and mercedes went the extra-brand route for their evs so far. Guess they want to make a premium-premium with a higher margin while keeping their classic bread and butter models around without cannibalizing their share.
Who will get a big problem though are all "less financially stable" non-premium-manufacturers. Those will have a BIG problem getting the neccessary funds to switch.