Haven't been terrible? He's borderline been better outdoors than in. It's a wash at worst.
Outdoors: 14.5 YPA, 64.3 catch %, 9.30 Y/target, 6.9 catches/game, 99.8 Yds/game, 25 TD in 49 games
Indoors (ballparking because of how Pro Football Reference splits out dome vs retroroof): 15.7 YPA, 64.4 catch %, 10.1 yds/target, 5.9 catches/game, 94 yds/game, 35 TD in 84 games
Sure, if you look at in a vacuum with no other information, but I think you would agree playing outdoors in Miami in October is a very different experience than playing outdoors in New York or Buffalo or New England in the last few months of the season. A good chunk of his outdoor games have been played at Carolina and Tampa, which isn't exactly the northeast, weather wise:
Last year, he played 2 games outdoors:
One was at GB, 4 catches, 32 yards.
One was at Carolina, 7 for 137 yards
In 2019, he played 3 games outdoors:
At Carolina, 6 catches, 91 yards
At San Fran, 13 for 134
At Tampa, 7 for 78 yards
In 2018, he played 7 games outdoors:
At Philly (game 1 of the season, 81 degrees at kickoff), 10 catches for 169 yards
At Pitt: 5 for 62
At Washington, 7 for 121 yards
At Cleveland, 7 for 107 yards
At Green Bay, 8 for 106 yards
At Carolina, 4 for 28 yards
At Tampa, 9 for 138 yards
In 2017, he played 6 games outdoors
At Chicago: 4 catches for 66 yards (week 1)
At New England: 9 for 99 yards, 1 td (4 catches and 32 yards, and the TD on Atlanta's final drive, down 23-0)
At NYJ, 3 for 74 yards
At Carolina, 6 for 118 yards
At Seattle: 5 for 71
At Tampa: 3 for 54
I don't have time to go a lot further back right now, but he has only played a handful of games in even mildly bad weather. The Green Bay game was 25 degrees, but they got blown out in that one and I think it was the Redskins game that year that was also below 40. Almost every other game I've looked at, even in bad weather stadiums has been at or over 55 degrees.
Don't get me wrong, I love Julio Jones and would give a lot of my own money to see him play in Foxboro, but I'm not so sure I want to be paying him 15mil per year during his age 34 season and watching him work the sidelines in 30 degree rain. It's just a different animal than sprinting down the field in the NFC South week after week in November and December. if they get him, I'll be extremely happy. But I imagine at some point, we'll be like, uggh, this is a rough end of the road....