Brown and Lampkin had nearly identical defensive rebounding rates last year (18.7% for Brown, 18.1% for Lampkin) but Colorado was very good at defensive rebounding (25th in the country) and we were very bad (308th) so I would buy the idea that part of the reason Brown's defensive rebounding was as good as it was is because he had no competition for defensive boards from any of his teammates.
Lampkin's block rate is troubling low for a guy his size, but Colorado wasnt great at block rate last year and still had a decent 2 point defense, while we were good at blocking shots and bad at defending 2s, so maybe there's some hope there. The positive spin is you're trading off some activity (Malik was great at steals and solid at blocks) for the size/positioning, but I have no idea if thats really true