Guess he made it to #1 for two years with the strength of his serve and volley game...
In terms of consistency, placement, ability to take the ball early Hewitt's groundstrokes are all very good, much better than average. The only way you could argue his groundstrokes were average or close to it is if you focus only on power. It should be obvious but you don't put up the kinds of return numbers he did without good groundstrokes, unless you think he had the GOAT return or something.
Hahahaha! Yes, excellent analysis. Only thing average about Hewitt's groundstrokes was power. Like the poster after you said, he was a baseliner who got to #1. The original poster asked about an "average ground game" not just the strokes. To say he had average "groundstrokes" but argue it was made up by speed and consistency is silly. You can't separate those things out from his groundstrokes. His ability to be consistent, his movement and ability to hit on the move IS his groundstrokes. If you focus only on how well he hits the ball standing in the same spot, I'm sure guys like Krajicek and Ivanesevic would outhit Hewitt. Make them move and suddenly their groundstrokes don't fare so well.
There's also a tendency to discount Hewitt's ground game by saying he was a good volleyer and won points that way too. Yes, he was a very good volleyer but NO, he did not win many points at the net. He was a pure counterpuncher. He didn't have the serve to come in often and didn't have the ground game to come to the net a lot. He was in many ways a refined version of Chang who was obviously a baseliner and a pretty competent one. There's also a problem of comparing generations. Hewitt's overall game was from a previous generation when pros believed they still needed a solid net game to reach the upper echelons. So he developed a good net game but this didn't make him any less of a baseliner. I think if you take a tennis fan of this generation and asked him/her to watch Borg or Connnors and never told them anything about their games, fans these days would think they were all-court players bordering on serve and volleyers. I don't think tennis fans these days realize how much players, even baseliners, went to the net.