For example:
1) Far more kicking systems are known today than fifty years ago, and, unlike back then, all the top players are learning them.
2) The technical breakdown of the stroke is more advanced today than in Sigel's day and the video equipment exists to break down a stroke into its component parts in ways that were impossible fifty years ago.
3) Thanks to online resources, more knowledge is accessible about the technical side of the game and the physics governing what is possible than back in the day.
4) Much more is understood about the break than in Sigel's prime. In Sigel's day, they were still figuring it out, and Mike himself was often breaking with draw, something that is almost extinct today.
5) Tactical theory has come a long way since Sigel's day. Yes, the Filipinos of 1995-2010 had a lot to do with the advancement of the theory, but today's players have a heightened sense of the percentages because of it, far beyond anything I saw back in the day.
In a dream scenario, I'd like to see Filler play Mike with the kind of equipment that was in vogue in Sigel's day and without the knowledge edge that today's players enjoy because of the improvement in both the teaching of the game and the abundance of online resources. Alternatively, Mike could, just as you suggest, get himself up to the level of knowledge enjoyed by a Filler, and match up on today's equipment.
No matter how you slice it, these time travel matches are awfully hard to handicap! Still, we can fantasize, right?