There is some truth to this statement. The need for a box-to-box midfielder has diminished since passing has only become more important and the ball always moves faster than a player. However, when comparing players of different eras, you have to compare their impact within their specific era. Ballack without a doubt had more of an impact back then than Thiago does now. He was absolutely irreplaceable. Thiago is a 'nice-to-have' player but Bayern or the Spanish national team did just as well playing without him. In Hollywood terms it is the difference between a main character and a supporting role.
I totally understand your opinion on Thiago, though, it's not an outrageous claim to think so highly of him. These hard-to-press ball distribution machine type of players are extremely useful in today's football.
Likewise, I can see why you rate Ballack that highly. I mean, he's a childhood idol of mine so obviously I hold him in high regard as well.
But yeah, impact in football is very hard to quantify. I believe Thiago and Kroos have more absolute impact on their teams while Ballack had more relative impact and that is because he played in worse squads. As I said, Ballack played in the Bundesliga during a very weak phase. Kroos would've been the best player in the league and in the national team by distance as well in that era. Same goes for Thiago. Ballack then went to Chelsea to play second fiddle to Lampard - and he was 29 back then, the same age Thiago is now, so he was still in his prime. IMO, Kroos was more important to a team that won three consecutive CL titles than Ballack was to a team that was good but still far off Zidane's Real Madrid side. And I think Thiago was just as important for Bayern last season as Kroos was back then. You can argue that he first should replicate that feat before you can put him in the same tier but then you can say the same for Schweinsteiger, for example.
I think another way to look at it is how they compare to other players of their era. Ballack was world class, no doubt, but I'd say throughout his career there were many CMs/CAMs who were better than him. If we only count box to box midfielders/center mids, then I'd say Nedved, Gerrard, Scholes, Keane, Davids, Viera, Deco, Pirlo and later on Iniesta and Xavi bested him from the top of my mind. But throughout his time at Bayern and Leverkusen, he played in a more advanced role and then you must compare him with Zidane, Ronaldinho, Kaka, Rivaldo, Lampard, etc. and in that case it's pretty clear I think. Yet it's very hard to name players who are ahead of Kroos during his time. He's quite clearly the best CM behind Modric since his move to Madrid and the two are the closest to Xavi and Iniesta under Pep we've witnessed. And Thiago comes next if you ask me. So Ballack is maybe a top 10 midfielder of the 2000 - 2010 decade while Kroos is clearly a top 5 midfielder of the 2010 - 2020 decade. Thiago edges the top 5 for me, too, but you can debate that. However, he's definitely in the top 10.
I also think Ballack wasted very important years in the Bundesliga to be honest. Between ~2003 and ~2008, the Bundesliga just wasn't a quality league. When Bayern brought in Ribery and later on Robben, that felt like an insane uplift in quality. I hadn't seen such players in the league up until then. There was also Diego at Bremen who looked like a world beater talent and the golden German generation consisting of Özil, Müller, Hummels, Neuer, etc. slowly entered the scene. Van Gaal as well who turned Bayern into a CL contender and gave them a philosophy. And Klopp's career began to really pick up speed around that time, too. Watching Ballack play never created the same feeling to me. There was suddenly a different quality and spirit of hope to German football. Meanwhile Ballack looked like a very good player for Chelsea but not the irreplaceable high performer he was for Bayern and Germany. I mean, there were so many players who played great in the Bundesliga during Ballack's time but it felt crazy to suggest they were good enough for top clubs. Ailton, Micoud, Marcelinho, Ze Roberto, D'Alessandro, Lincoln, Makaay, Klasnic, Klose, Rosicky, Hleb etc. all dominated the Bundesliga but at times didn't even make their national teams let alone making their starting eleven. That is important context, especially since Ballack quite obviously didn't stand out at Chelsea. Sure, Bayern did it for the longest time and was regarded the best player of the league back then but at times he was bested, e. g. by Micoud or Hleb, over the course of a season. That's very important context for me when ranking Ballack.
