It was certainly a risk/reward that hasn't exactly panned out the way we wanted.
The good, optimistic hypothetical was that DM would ensure we get more playoff exposure, accelerating the development of the young guys. But also taking pressure off them in the regular season so they can develop in that regard. ofc much different situation but Kyrie and TT only had three seasons under their belts before we got LeBron. I don't think Kyrie and TT's development were held back by LeBron.
Also there's the thought that any time you are able to get a top 15 player, or however highly you want to rate DM, you do it. NBA is an asset-driven league, DM is a great asset.
You also can't say that its a foregone conclusion that we'd be a playoff team without DM, and that a frontcourt of LM/EM/JA would carry us. Mobley and JA have not played well together this year. Is that because other teams have figured out how to defend them, or some other reason?
If I'm starting from scratch though, I sure would like my lead "point guard" or "combo guard" or rather "smallest player on the court with a high usage" to be 6'3 with a 6'10 wingspan, excellent athleticism, and built like a brick shithouse, as opposed to Garland, even if DM's not as "pure" of a PG.
But the story is not over yet...