I agree that both helped each other, but if you think that line made Emmitt better than he truly was, then maybe you need to be reminded of what he did once that team became average then dipped even lower and became complete shit.
By 1998, Cowboys were nowhere close to being a great team and that line wasn't anything special, but this is what he did that year: 1,332 yards rushing, 13 TD's, 2 TD's receiving. People were beginning to wonder after a tough 1997 if he had anything left. He proved in 98 that he had plenty left.
1999, at the age of 30 and on an 8-8 team with no Michael Irvin, and no Troy Aikman for a good part of the year, he put together one of the most impressive seasons of his career.
He led the NFL in 100 yard rushing efforts with 9, ran for 1,400 yards, rushed for 11 TD's and again, scored 2 TD's receiving. This was the season when teams began loading up the box because they had no reason to respect the Cowboys passing game, and yet, there he was having his best season in over 3 years. Remember that awesome night against the Vikings where he ran for 140 on the 1st half? He did that with Jason Garrett playing QB.....just sayin'.
2000 - this is the year where the Cowboys became total shit. No QB, no passing game, and Emmitt at the age of 31 ties an NFL record with his 10th straight 1,000 yard season. 1,200 yards rushing and 9 TD's.
2001 - this was probably the worst of those Campo teams. I mean, they had Quinthy at QB for crying out loud. There are no weapons on this team to speak of, but that doesn't stop Emmitt from setting an NFL record with his 11th straight 1,000 yard season......and keep in mind that he is 32 years old when he does this.
2002 - the first signs of decline, but like 2001, he is the only halfway decent offensive player we have and yet he still gets to week 17 with only 20 yards needed for another 1,000 yard season, but unfortunately, the O-line was awful against the Skins and he only gained 13 yards on 18 carries. While he didn't get his 1,000, it's clear that he wasn't just limping along. Most guys by this point at 33 are struggling to get to 800, but Emmitt was still a productive player for the Cowboys.
To me, what he did in his 30's, between 99 and 2002 on awful teams with bad O-lines, speaks volumes about how great he truly was. If you don't think he was equally responsible for his success in the early 90's, then we'll just have to agree to disagree.