There's no way you can think the 2nd tier now is worse than in the early 2010s. If players in the 2nd tier include David Ferrer and JMDP, then take for example in 2012, Ferrer finished the year ranked #5 with 76 match wins and 7 titles, and JMDP finished the year #7 with 65 match wins and 4 titles. Outside of Carlos, no one this year has a chance at reaching 65 match wins (the 2nd most is Alex De Minaur and Alex Zverev, with 35 and July is finished).
Back in the Big 3 days, you needed close to 50 match wins to finish in the Year End Top 10. There's a chance that Carlos is the only player that reaches 50 match wins this year.
You're taking one metric, match wins, and applying it to only a comparison of 2025 and 2012. We can mess with numbers all we want, but we can't define any era by a single year, or arbitrary narrow comparisons and single stats.
Anyhow, I haven't made up my mind either way, as far as the 2nd tier now (or say, the last half decade) vs 2010-15ish. At the least I think it is arguable, and depends upon which specific years. It is a bit like trying to compare two paint splatters for coverage: the patterns are too different, the talent dispersed differently.
On a side note, I am reminded of a recent conversation between Andy Roddick and Chris Eubanks in which they talked about the game changing within the last year or so, with players hitting the ball harder than before. Maybe it is rackets, or maybe we're going into an era in which players play even harder, but with less matches played. Sort of like how in baseball, only a handful of pitchers throw 200 innings, when that used to be the baseline for a full-time starter. The average fastball has increased by something like 5 mph in the last 10-15 years...which is a huge increase, and it is leading to fewer innings.
