I can't embed the heat map for Alli vs Watford but it clear shows he was hardly ever in the opposition box, he's clearly mostly outside the box. A lot of detractors want to make out that Ali is nothing but hype, I assure you he is not. His build up play and passing is excellent, maybe not the longest range of passing but he creates space and moves the ball on well. He's not a dirty player but very rash, he's a winner, think Rooney at the same age.
Thing is heat map doesn't fully describe a role. No 10 heat map, which is more midfielder than second forward, can be very similar to second forward. The difference is in game you can see that traditional no 10 tend to stay behind the tip of the formation, even in counter attack, as no is the play maker. Second forward makes off ball movement and take the tip of the formation at times (aka the term forward), to receive the
Heat map ain't accurate as some team try to lure other team out instead of overloading the box. You have to compare player position in game. The off movement, the position they receive the ball compare to the formation of the team... It can be like this: the targetman not always stays in the box, but drop deep to hold up play out side the box. Second forward make run beyond the target man, but still not enough to make it into the box. The "midfielders" may have similar heat map but in the move described above, these midfielders often behind the second forward who make the run beyond and become the tip of the formation.
Edit: If you compare heat map between Tottenham & United, you can see that the style are very different. we put man more into opposition box, while Tottenham seems like working mostly outside the box with much less heat in the opposition's box. If one said Tottenham doesn't attack by citing heat map, it's wrong. Tottenham style is exploiting pocket of space vs ours to supply the players in the box. Ours individual players' heat maps are easier to read as the distinct
To quote myself compare a second forward vs no 10 (Griezmann vs Kaka) from another discussion in other thread.
You must be remembering thing different for those players. Griezmann made a lot of off ball run behind the defense even if he start behind the main forward. Kaka, Del Piero, VDV main area of operating were always behind the forward. Picked up the ball from midfield and bridged the gap between midfield and forward lines. They were part of midfield operation. Griezmann Alli, Muller, Totti since Spalletti more often than not would be the furthest point of the formation when the team are in possession.
Edit:
There is no absolute, but Griezmann in most game much less getting involved in build up this deep; while this used to be the norm for Kaka. See that he didn't rush to be the furthest of the formation even after the ball was spread wide despite being in position able to do so (indisciplined if doing so as it's not his job). Solely stationed behind the forward
Edit 2:
Compare for example to this a game where Atletico would have to play deep vs a better possession team, which assuming he had to operate deeper. Even with another striker, Griezmann touches were mostly very close to the tip of the formation, and actively try to rush into furthest/ forward position and leave the midfield & play making to other.
Edit 3:
Since the Barcelona game maybe unfair given Atletico didn't do well, so on the second thought, I picked another game here where Griezmann was the MotM.
Got more involved, but the point stood that he made more off ball movement behind the defense & trying to be the furthest player of the formation than supposed no 10.
I will add from the initial post that youtube video only about touches, yet in many cases it's sufficient to make the point in this case. There are more runs that don't result in touch during game. But it's very clear in game the contrast between no 10 & second forward off ball staying behind the tip of the formation vs off ball movement to be the tip of the formation.
There what
@Zoo said about Lampard's analysis.