I'm fine if Sigma copied the best 50mm lens ever made.
"Imitation is the sincerest form of flattery."
I think it's too strong to say that Sigma 'copied' Zeiss. Manufacturers keep an eye out for technology from the competition and try to learn from them as well, but 'copying' is generalising too much. Sigma has incredible lens-design know-how (it is their core business!) and recently they decided to up the ante - and also the price of the new products. It's not as if Sigma suddenly became better at lens design, it's the way they approach the market that changed.
5D3, 5D2, Sony α6000, G16 | EF: SY14/2.8, V20/3.5, 28/2.8 IS, Ʃ35/1.4, 50/1.8, 50/1.8 STM, Ʃ50/1.4 EX, 100/2.8L IS Macro, 16-35/4L IS, 24-105/4L IS, 70-200/2.8L IS II, 1.4x II, 2.0x III, T28-300 VC PZD, 70-300L IS, Ʃ150-600 OS HSM S | E: SY12/2, 35/1.8 OSS, 16-70 ZA OSS, 55-210 OSS, SY300/6.3 ED UMC