I agree on the diagnosis having driven both within a week when doing my purchasing decision. But like Darren says... not similar money. Don't forget Telsa price includes £5,000 grant and BMW doesn't. You'll have a few extras to pay for on the Telsa too before you are happy with your spec. Like autopilot £2,200 for active cruise and subzero pack £850 - for heated washer jets..
Also don't get fooled by Telsa's equivalent price - which means petrol savings and tax knocked off... as the i3 gets those too.
The real cost of a base spec S70 RWD is £51,180. That's £20k more than a base spec i3 (if you are comparing like for like). For that money you could get a spare VW T5 van AND a Lotus Elise....both used but then you have all bases covered ;-) Commuter, holiday load shifter bus, and weekend/track car.
For me the issue wasn't just cost it's what did I really want? I decided to hang on and get a top spec Telsa in a few years... assuming battery range would increase (correct) and that prices would come down (correct). And that for now... the i3 would make a great commuter car which with a REX doesn't have to worry about battery degradation ever so I can pass it on to my mrs in 3 years and then my 9 year old son when he's 17. Can't see me giving him a 300hp Telsa cruise liner! LOL.
The not so top end Telsa S85 I was speccing to keep the price down came in at £63,000. My upgraded i3 cost £33,000 after grants (I spent the equivalent of the grant on extras LOL). . When you add the interest of a PCP deal - just the interest on the Telsa was £10k more over 3 years. Hence I'll wait till I can afford a cash purchase on that one!