I am sorry if this is a stupid question, but is your concern that there is an actual developmental problem that won't self resolve in time, or that asynchronous development is causing him deep frustration and behavioral problems?
My 2nd child people regularly commented how remarkable it was to see a child so determined to do things beyond their present abilities and yet so sunny natured. Even before she could talk she was incredibly good at getting what she wanted. And now although she has an almost DYS level VCI we think she has selective mutism, or is recovering from and now has meer "social anxiety". She has a huge vocab and language development but will do anything to avoid talking if she can. So being happy not to use her prodigious language skills has maybe not been that great after all.
My 3rd just bellows. ALL the time. Doesn't even try to communicate often, just goes straight to bellowing. I suspect she might actually be "brighter", but with a speech impediment, it's hard to tell for sure at 15 months! Honestly I feel most of the time like she is trying to communicate psychically and is really pissed I am not "listening" and so she screams. As crazy as that may sound.
Child #2 was easier to parent with regards to communication, but she had other challenges (like scaling tall bookshelves the second you turned your back). Child #3 is less likely to break herself or something valuable but is really exhausting on the communication front. My point being, unless you are concerned that there is a problem that is beyond the realm of "it just takes time for them to grown into their skills sometimes" I think this falls into parenting an asynchronous toddler is damn hard work...
And my apologies if I have gone off on a completely irrelevant tangent.
