At his peak Lee weighed 160lbs.
He was a devastating striker and yes, he could grapple with the best of them.
He could not grapple with an equally-good big man. Good big man > good little man. Every time.
If both have equal grappling "ability" or "technique", the bigger, stronger man wins every single time, barring some total fluke.
Any of today's good MMA guys would pwn Lee so easily and quickly that it'd be embarrassing.