First off, let's talk about 2017. The investigation found that the two people who brought the sign stealing scheme to Houston were Carlos Beltran and assistant coach Alex Cora. Both joined the team for the 2017 season. So they were not cheating before then. If you look at Altuve's stats, he hit .338 the year before in 2016, .313 in 2015, and .341 in 2014. He can just rake.
Let's talk a little more about Altuve and the cheating scandal, since many seem to want him to be the face of it. Based on the evidence, Altuve was clean.
Look at his home and away batting splits in 2017. At home he hit .311, but on the road he hit .381. Every single stat of his was better on the road. Carlos Correa has said that Altuve did not use the sign stealing scheme, and refused to participate. Here is that interview:
https://www.youtube.com/watch?v=Waxx9kLqnlc
Here's the transcript of Correa in that interview:
And the evidence seems to support that admission from Correa. Here is a chart from a guy who plotted every trash can bang he could from the 2017 season. Here is a comparison of Altuve to some others, such as Marwin Gonzales and George Springer:
There is a video out there where you can hear a bang when Altuve is up to bat, and he looks at the Astros dugout and looked pissed off. I honestly believe what Correa said is the truth. He has been very candid through the whole thing. Edit: Here is the video of Altuve looking pissed at the dugout after a bang: https://twitter.com/adams_at/status/1402342356456722434?s=21
As for the sign-stealing scheme as a whole, there isn't really any evidence that it worked to begin with. If you look at the stats, the Astros hit .279 at home and .284 on the road. Every stat was better on the road than it was at home.
The truth seems to be that the Astros can just flat-out hit. They thought this sign-stealing scheme could make them even better, but in reality at best it seemed to have very little effect at all. I think it's been proven not only in the stats, but also that their team can still absolutely rake even after all this stuff came out.