Not true. Neither Jones nor Alex really improved.
TJ's production dropped in every category his second year, and his draft stock declined a bit as well.
And the best Poythress ever looked was at the beginning of his Freshman year (especially that Duke game). It was downhill from there (and his draft stock ended up completely crashing, falling from a projected high lottery pick as a freshman to not getting drafted at all).
Jones' production dropped because the entire team got better. Lamb played better. Miller played better. The lobs that went to him were split between 3-4 guys.
He absolutely improved. Remember as a freshman the awful shots he would take from the perimeter? Or when he'd pump fake four times and fall back and get his shot blocked from three feet? Or when he'd over help and leave a wide open offensive rebound? Or when his shot wouldn't fall and he'd pick up two cheap fouls quickly trying to steal the ball from the guy who rebounded his miss?
Poythress kept his scoring and rebounding averages roughly the same freshman/senior year, cut his turnovers in half, and shot better from the floor while playing better defense. His win shares stayed the same but his box plus-minus tripled as a senior. Some regression.