Eaxctly, the game is changing an tbh it has always been this way. It's more important that a team has a quality talent than a player who is simply good for his position. Look at our best teams and players, most of them were great and played in different roles. People always act like this is an Ajax thing, but its true for most top teams.
At United alone, we've had Ronaldo, Rooney, Giggs, Scholes, Beckham, Ole, Irwin, Ole play in multiple roles. We have also had versatile squad players like Brown, O'shea, Park and Fletcher do the same. This feature allowed us to have teams littered with quality despite suffering injuries to some of our best players at different points.
In today's game, City, Liverpool and Bayern all have extremely versatile players starring in their teams.
City's entire frontline last season all had spells at the 9 role. Foden and Grealish could also play in one of the attacking midfield roles. Cancelo could play in either full back areas. DeBruyne and Bernardo Silva could also play on the flanks. Gundogan would come in at times and could play in anyone of the 3 midfield roles. What mattered the most was the fact that these players had the quality in different facets of their game to play different positions. Whereas for us, we couldn't even get Martial or Rashford to play on the right flank. Ronaldo did not play in any position outside of the 9 role.
Liverpool challenged City. They have three strong centre back choices. Milner and Oxlade can chip in in any position that is required. Henderson can comfortably take on the DM role when needed. Diaz, Salah, Jota and Mane could all play across the front line. Firmino could also come in an play as a 10 if required. Rather than simply have decent players for each position, they focused on attaining great quality players that were hard working and versatile enough to play in different roles whilst ensuring depth for the team. Whereas at United, our fans are already complaining about where Eriksen will play despite the versatility other teams have. Some are crying about VDB not playing his "ideal" role.
Bayern take this a step further. Lucas Hernandez can play LB and Centre back. Alonso Davies can play full back, wing back or left wing. They have Pavard who can play right back or centre back. Kimmich can play on either role in midfield or at right back. Gnabry Musiala and Muller can play right wing, AM or left wing. Sane can play on either flank as well.
What is important is that a team has good players, good players that can fulfill certain duties the manager wants. Not necessarily their role. Martinez brings a stopper who can cut out counter attacker, whilst having the ball playing ability to get the ball consistently into the midfield area. Currently, we don't have this type of player. Also add to this, Ten Haag builds up with 3 players at the back with either a CM, LB or RB coming in to support the two centre backs. Having 2 of Varane and Martinez always being in that position gives us a good amount of quality in the build up.