A solid TE and a good RG can bring the offense to at least an average level. One of the things not mentioned is that we had a somewhat healthy Long in 2018. When he was effective, our run game was more effective. We never had an answer for RG in 2019. Long was hurt, and there was no-one that really stepped up to fill that role.
Better quarterback play would fill holes. A threat at QB will make the receivers better, give the RB some room, and make the O-line look better. But, if we don't get better QB play, then we'll need better receivers, depth at RB, and an improved O-line. That's all in addition to getting a TE and RG.