Under the knowledge that Piccolo believes Super Boo will take some time in killing the humans, than it is a foregone conclusion that he believes normal Earth training is still effective. The way I have always seen it is that Gotenks Pre-Rosat was more-or-less a work in progress. His brief 6-7 days of training in the Rosat gave him that extra push he needed to secure his victory over someone of Innocent Boo's calibre -which is implied when Super Boo fights him at that battle power.
Prior to Super Boo's arrival, Innocent Boo became more docile and warm hearted, he didn't want to kill. Hence why Piccolo wasn't entirely concerned about him anymore and he definitely did have the adequate time to prepare Gotenks for that final battle. Albeit, Gotenks only had to go a little further then where he was previously at.