My DS was very much like this. It's good that night sleep is not too bad - that's something at least (most of the time)
It's hard to know, and only you can ultimately judge, but I certainly found there was no point in trying much. Just made my life harder.

There was always a reason why he couldn't sleep - developmental, physical, whatever. Things improved markedly for day sleeps after 15-16 months. Night sleeps he slept through for the first time at 19 months, but still needed ltos of help going to sleep. It wasn't till nearly 2 that he stopped fighting it all the time

The only thing that helped me was finding ways to cope better, rather than trying to change him. We coslept a lot. We used the HAB (sooo hard wen you have stay upright and moving - DS was the same). I walked him to sleep. I timed outings for sleepy times. Till 15-16 months, he rarely slept longer than 30 mins at a time during the day. No matter what.

so, in sum, I have no real advice for you.