Unseld was definitely one of those guys who's statistics didn't come close to showing the effect he had on winning and the game in general. Dave Cowens comes to mind as another guy from that era that was the same way.
Aaaaand peak Dave Cowens was amazing when it came to good old statistics
. The narrative that "statistics will never measure everything on the court" needs to change into "what statistics are being used and what are they measuring", peak Dave Cowens killed it even with the fuzzy data we have in the 60s and 70s - he was the defensive anchor of some strong Celtic defences in the early-mid 70s, was likely a big contributor to a sizeable SRS jump for his squad even as a rookie and caused his team to fall off a bit as his peak ended in the mid-late 70s (his early demise + the excellence of Hondo deflated his +/- numbers, but the wealth of team signals as well as his box stats that reflected his skillset as a floor spacing, high post passing big who played strong defence and dominated on the boards capture his value pretty well).