Ruth and Gehrig...
Aaron and Mathews...
Mays and McCovey...
Lindor and Ramirez?
Alright, so Francisco and Jose (proabably) won't become as storied as those other pairs of teammates, but don't sleep on how good they've been. They're posting numbers few duos ever have, even before taking into account their defensive positions. With Lindor at shortstop and Ramirez at third base, this year's Indians may have the best left side of the infield in baseball history. Seriously.
(In looking at top twosomes, I'm focuses on the figures both members cleared, rather than just adding the two players' individual totals together. This is so as to avoid what I think of as the Stacey King factor. King was a backup center on the Bulls for the first three of their six NBA championships during the 90s. Michael Jordan once scored 69 points in a game against the Cavs; afterwards King told the media, "I'll always remember this as the night that Michael Jordan and I combined for 70 points." It was a fantastic line, but speaks to the flaw in simply combining.)
Only one team has ever had both its third baseman and shortstop post a wRC+ of 150+ in the same season. It was the 1898 Baltimore Orioles, so perhaps President McKinley can tell you more about it. The teammates were John McGraw and Hughie Jennings, and at 153 and 151, respectively, their wRC+ figures still aren't quite as strong as Ramirez and Lindor's right now. In the 120 years since then, the closest any left side of the infield has come is Lou Boudreu (166) and Ken Keltner (144) for the 1948 Indians. In the 70 years since then the top duo is Hanley Ramirez (144) and Miguel Cabrera (142) for the 2007 Marlins.
Ramirez and Lindor currently lead MLB in extra-base hits, with 54 and 53, which puts them on pace for 96 and 94 of them. No third base/shortstop tandem has ever had both members reach 90 extra-base hits. In fact, only one third base/shortstop tandem has ever had both members reach 75 extra-base hits. This time we don't have to go back very far to find the top pair, because it was Ramirez and Lindor a year ago, when they put up 91 (a record for any player whose primary position was third base) and 81 extra-base hits. (Like I said, they've been better than you may have realized.)
Ramirez and Lindor probably won't both end up with 90+ extra-base hits, but if they do, they'll join Gehrig and Ruth in 1927 as the only teammates to do it, regardless of defensive positions. If they both reach 80, they'll join Gehrig and Ruth (1926-1928) and Gehrig and DiMaggio (1936-1937) as the only teammates to both reach that total in consecutive seasons. Company scarcely gets any more impressive than that.
I grasp the dangers of discussing what players are on pace for (though it's not as if we're talking about guys two weeks into the season), and understand that both Ramirez and Lindor are likely to fall short of their current pace. If you prefer first-half totals, Todd Helton and Preston Wilson with the 2003 Rockies and David Ortiz and Manny Ramirez with the 2004 Red Sox are the only teammates at any positions to both have 50+ extra-base hits by the All-Star break. For a third baseman and shortstop, pair, Ramirez and Lindor last year are the only one with 40+ each.
Ramirez's 27 home runs (second in MLB at the moment) put him on pace for 48. Lindor (tied for third with 25 right now) is on pace for 44. No pair at their positions has had each member hit 40 home runs in the same season. And they have some margin for error in terms of becoming the top home run hitting left side of the infield, as the highest mark reached by a team's third baseman and shortstop is 34, by Eric Chavez and Miguel Tejada for the 2002 Athletics.
Regardless of position, if Ramirez and Lindor do both reach 40 home runs, they'll be the youngest teammates ever to get there in the same season, as Ramirez is currently 25, Lindor 24, and every other tandem who pulled it off had at least one member who was 27 or older.
Using wRC+, extra-base hits, and home runs, Ramirez and Lindor's 2018 is on track to become the best season by the left side of any infield in history. Even that sort of sells them short though, because unlike a lot of the third basemen and shortstops who populate offensive leaderboards, Ramirez and Lindor are both strong defenders at their position, so their even better than their impressive hitting makes them look.
At Baseball-Reference, Ramirez is already at 6.0 WAR, Lindor at 5.2. The issues with using pace for WAR are probably even worse than with using pace for more traditional counting stats, but I'm still going to mention that Ramirez is on pace for 10.7 WAR, Lindor for 9.3 WAR. The only position player teammates to both post 9+ WAR in the same season are Nap Lajoie and Terry Turner in 1906, Gehrig and Ruth in 1927, 1928, and 1930, and Ken Griffey Jr. and Alex Rodriguez in 1996.
Even if you lower the bar a little to include teammates who each reach 8 WAR in the same season, it's only happened 14 times, with Albert Pujols and Scott Rolen in 2004 as the only duo to accomplish it in the last 20 years.
Alex Rodriguez and Derek Jeter, the most famous left side of an infield in my lifetime, never both had more than 4.5 WAR in the same season as teammates, which means Ramirez and Lindor have already topped those two, despite not having yet reached the All-Star break.
Going back to left sides of the infield, the highest mark both members have ever reached in the same season is 7.1, and now we're going back to the 1898 Orioles again, when Jennings was worth 7.5 WAR, McGraw, 7.1. For an American League left side of the infield, the highest WAR figure both members have reached is 6.4, by Alex Rodriguez (8.4) and Hank Blalock (6.4) for the 2003 Rangers. Ramirez and Lindor could both be above that mark by the middle of August, when there's still a quarter of a season to play.
They're already the first left side to both put up 5+ WAR in consecutive seasons since Eddie Mathews and Johnny Logan for the 1955 and 1956 Milwaukee Braves.
Bad health is about the only thing that can keep Jose Ramirez and Francisco Lindor from putting up the best year any left side of the infield has ever had, and if they maintain something close to their current pace, it'll be worth dropping the left side of the infield part of it, and assessing where they rate among the most season by any two teammates in history.