I'd agree Max had the line, and Russell did not have his car established "substantially" alongside at the moment of contact. That's not not set in stone but usually taken to mean the leading wheel at least half way between the 2 wheels of the car being overtaken.
Russell had been up alongside, perhaps fractionally ahead a moment prior, but Max had the line as was thus carrying more speed so by the moment of the impact a second or so later his front wheel was barely in front of Max's rear, thus not substantially alongside, thus regardless of who had the line it was his duty to yield in the sporting regs. Watch the footage on Sky Sports website, Max is well aged a the crucial moment of contact and that is the key metric in the absence of other factors.
However, I don't even think its a case of failing to yield, more a case of Russell understeering just a little on cold tyres. Had his tryres been up to fulk operating temperature I think hed have gripped and pulled in behind Max to either try the slipstream or keep within range for a later DRS attack. However, I - and the Marshalls - don't think Russell was being reckless. Its wasn't much of a slide, cold tyres and all that. Racing incident. Even Toto Wolff has expressed sympathy for Max on that one, while diplomatically not condemning his own driver.