I realize I'm jumping into a debate between two people that are not me, so sorry, but I wanted to emphasize what
@Mach2 said about positional value.
It is true that LT does have high positional value, and the argument is that because Tua is a lefty his RT is his blindside protector has high positional value does have merit. But, most defenses are designed to isolate their most elite speed rusher against the LT most of the time and their most powerful bull rusher against the RT most of the time. So I think
@Mach2 is correct regarding Sewell's positional value. Most teams would be content to keep their bull rusher against Sewell at RT and take their chances generating blindside pressure, and isolate their twitchy speed guy against Jackson, who hasn't quite evolved to become a dominant LT yet. The increase in efficiency by adding Sewell is significant, but not a game changer to this offense. Tua's mobility is one reason why we do NOT need to invest in two 1st into OT just to get a solid line.
Jesse Davis + Ja'Marr Chase >= Pennei Sewell + Preston Williams. That is the equation. And realize that whomever is NOT replaced in either side of this equation is a strong candidate to be replaced in the 2nd round of this or a near-future draft. Chase has a chance to make this offense great. Sewell has a chance to make this offense solid. I know which I'd choose.