It's not about Marv being better than a late first-- it's about making a move to secure a higher draft-pick in a season where we won't be making the playoffs, and get some sort of return in the mean-time.
I understand that keeping Marv here for the entire season gives us a better chance of picking him up again in the offseason (as opposed to trading him, then trying to bid for him again)-- but we got to figure out our priorities:
Would we rather have a worse record, and draft a player like Jabari? Or do we want to take a gamble with a 7th-10th pick, and secure a decent stretch-four?
Personally, I see the most glaring hole in our roster being a lack of a consistent scorer, or a player we can build an offense around. Consequently, clearing up cap-space and acquiring more tradable assets while worsening our team record seems to be the solution here.