Thanks everyone for your input, especially your very considered response @FATEdestiny. Rocking him to sleep then putting him down has never been a problem, he's always slept really well from being little, so that's how we got in to it - but I can see how now he's older that might be a problem. I never thought about how inconsistent it all it (which is often due to having to put my toddler to bed at the same time), that's really eye-opening.
Yes, @Muststopeating, I know the logic too, but it's very hard to put into practice!
I also didn't think about his daytime sleep improving - the short naps are hard, he gets very tired and cranky A LOT, and we end up with an inconsistent routine all round. It's difficult, though, isn't it? They aren't (well, mine aren't!) robots, and he wakes up at different times in the morning, naps are different lengths, he's not great taking milk so we are having quite a lot of solids so there's a lot going on for him, poor little thing. Now that I think of it, I barely have a bedtime routine for him, and some nights I'm just trying to settle him and bung him down asap to get to the toddler