ABA has helped my son to maintain the gap between him and his peers, narrow the gap in other respects and also catch up. But he hasn't completely caught up across the board by any means. We started ABA when he was 3.4 and he is 4.7 now.
He has a very spiky profile, and when we started, he was very delayed across the board. For example, his language was plotted as 0-11 months. We introduced PECS as part of his ABA programme, also signing and then finally his language came. There is some functional and observational and expressive language in there, but also a lot of echolalia. His language is now at about 2.5-3.3 I think.
When we started, his problem solving skills were 11-18 months. He is now age appropriate, doing jigsaw puzzles and peg board puzzles quite happily.
When we started, his self care was 11-18 months (I think). He couldn't get dressed or undressed, and was in nappies as he had no awareness of weeing or pooing and wasn't remotely bothered by being dirty or wet. He is now toilet trained, can undress himself but cannot properly dress himself.
Are you considering ABA for your child, or are you doing it? Our experience of it has been fantastic.