He was Matthews most consistent linemate so it should be expected hat he has the most assists with him.
Replace Hyman's icetime with another player and they too would be expected to have the most assists with Matthews. THat number in of itself doesn't really tell us anything about Hymans effectiveness or lack there of
This can be proven with some very basic math.
Nylander got about 55-60% of Hyman's TOI with Matthews and has about 55-60% of Hyman's first assissts to Matthews. His total assists relative to ice time with Matthews is even better than Hyman's.
I liked what Hyman did for Matthews in terms of puck retrieval. I don't think any Leafs fan is disputing that.
However, I don't think Hyman was any kind of exemplary playmaker for Matthews (based on these assist #s and actually watching 88 games of them together) and the BIGGEST issue is that he shot 4.5% when playing with Matthews (and despite being among league leaders in high danger chances) which is just abysmal. I think that's most Leafs fans biggest complaint of Hyman as well, but big surprise that this factual concern is being clearly deflected and obfuscated by pointing to assist numbers which literally have absolutely nothing to do with Hyman's own finishing ability.
Big "W" for obfuscation today.