I was digging into Anderson's spin rates in comparison to the rest of the league and it's ugly. Of the 325 pitchers to throw curves and record at least 100 PAs, Anderson's spin rate was 324th. A measly 1874 RPMs. Since the start of 2020, Anderson's curve ranks 859th out of the 870 pitchers who have thrown curves and recorded at least 100 PAs. That's 1.3 percentile.
In order to get into the top half of the league in spin rate on a slider last year, you'd need 2,422 RPMs. None of the 21 pitchers who had a curve spin rate under 2,100 RPMs last year had a slider in the top half of the league in spin rate. Of the bottom 100 pitchers in curve spin rate, only 5 had sliders in the top half of the league in spin (67 of the bottom 100 in curve spin threw sliders as well).
To be in the top half of the league in curveball spin rate you'd need 2,465 RPMs. None of the top 25 in slider RPM last year had a curve ball with a spin rate under 2,500 RPMs. Only 9 of the top 100 in slider spin rate had curves that ranked in the bottom half of curve spin rate (60 of the top 100 threw both pitches).
Since the start of 2020, 35 pitchers have averaged a curve with a spin rate under 2,000 RPMs. None of them have a slider averaging 2,400 RPMs or better.
I say all this to show there's a strong correlation between slider and curveball spin rates. It makes sense as they're both breaking balls with similar grips. Considering how heinously bad Anderson's curveball spin rate is, I see no chance his slider is even league average. Unless he's a crazy outlier, we're looking at a fringy pitch at best. Another fringy breaking ball isn't going to change Anderson's results.