Yeah, neither Harris nor the still-young Maxey nor Hield can make up for that loss, not even compared to Butler, Simmons or Harden from past teams when Joel was out (at least in the regular season).
Even when Joel is back the obstacles remain large. Losing in the play-in, losing because the first-round seed is tough, or just the usual second-round exist. Of course there's still a best-case scenario too, but for now, more of a dream.