Grant can't guard 3s. He does have defensive value, but similar to Roco its more as a help defender, not one on one against wings. Grant doesn't rebound like a 4, he rebounds like a short PG. He is efficient offensively.
He definitely has value in a rotation, but he's sort of a quirky player that has odd strengths and many weaknesses to his game. For a reasonable salary he is great, but with rumors of him making $30million+ per season? Might end up being a player worth less than his contract like Nurk.
If Blazers want to contend they need a defending SF like Bridges or Brown. Siakam while good defensively is an awkward fit next to Grant.