Howell Heflin was actually slightly more Conservative than Shelby when the latter arrived in the Senate in 1987. They both scored a 46 and a 43 Conservative rating from the ACU, respectively. Of course, by 1996, Heflin was still at 40, but his overall lifetime had declined to 30%. Shelby was over twice as high, then a 90%. He has since deteriorated to a 68%. The leftist Jones that Shelby supported over Moore got an 18% in 2019.
With a lot of these establishment cretins, they peak and start moving leftward in time, as Shelby has done. Since after 2011, he has only scored above 90% once, in 2015.
Again, if you compared Zig Zag Dell’s ACU rating to Paul Coverdell’s, I think the results were similar. Coverdell scored near perfect ratings year after year. I think Zig Zag got to 90 once or twice, near the end of his tenure when didn’t have to run for re-election as a RAT. Earlier in his Senate career, he was “very conservative” by RAT standards, but didn’t even get close to the ACU rating of a typical RINO.