I can only give you subjective opinion, it's what 99% of this message board is about. Your request that I prove it by video analysis is silly.Thanks for your considered response and telling me that I'm all over the place.
So in short you have no specific evidence that Sanchez has lost his speed, just the 'Hundreds of videos of his game that are out there'? OK, seeing as you have no factual evidence to provide to back up your opinion, & seeing as there's 'hundreds' of videos out there which you've found the time to reference, you won't have a problem finding 3 or 4 and posting them with a detailed analysis of how you intend to compare his pace from his time at Arsenal until the present then?
Also, in a failing team Sanchez managed 30 goals in all competitions last season, with 24 of those coming in the PL which comfortably made him Arsenal top scorer by 11 goals over his nearest team mate. Do you care to explain how this is classed as 'His fading' over this season and last?
The season before he was only 2nd to Giroud (24) on 17 and was still 8 ahead of his nearest team mate Walcott, so did you have an issue with Sanchez in 2015/16 too?
Players grow old, and those who rely significantly on power/pace are particularly affected. I predicted in the Summer he'd struggle to replicate his form of last season and he has.