Here's the way I think Superman can make around the same or potentially more than The Batman.
Adjusted for inflation opening for recent Superman films + every Gunn CBM :
SUPERMAN RETURNS 80,014,651.60
MAN OF STEEL 154,394,990
GUARDIANS 1 122,880,186
GUARDIANS 2 184,343,206.37
GUARDIANS 3 118,414,021
THE SUICIDE SQUAD 26,205,415
Take the average of that, which would be: $114,375,411.76
Legs for Gunn's Guardians films.
Guardians 1: 3.54
Guardians 2: 2.66
Guardians 3: 3.03
Average: 3.076666667
And depending on the international/domestic splits, here are a few different scenarios basing on the MoS DOM/INT split and the Guardians films splits:
MAN OF STEEL SPLIT
SUPERMAN (GUARDIANS 1 LEGS)
920,202,176 100%
404,888,958 44%
515,313,219 56%
SUPERMAN (GUARDIANS 2 LEGS)
691,451,353 100%
304,238,595 44%
387,212,758 56%
SUPERMAN (GUARDIANS 3 LEGS)
787,630,676 100%
346,557,498 44%
441,073,179 56%
SUPERMAN (AVERAGE LEGS)
799,761,402 100%
351,895,017 44%
447,866,385 56%
GUARDIANS 1 SPLIT
SUPERMAN (GUARDIANS 1 LEGS)
941,602,227 100%
404,888,958 43%
536,713,269 57%
SUPERMAN (GUARDIANS 2 LEGS)
707,531,617 100%
304,238,595 43%
403,293,022 57%
SUPERMAN (GUARDIANS 3 LEGS)
805,947,669 100%
346,557,498 43%
459,390,171 57%
SUPERMAN (AVERAGE LEGS)
818,360,504 100%
351,895,017 43%
466,465,487 57%
GUARDIANS 2 SPLIT
SUPERMAN (GUARDIANS 1 LEGS)
899,753,239 100%
404,888,958 45%
494,864,282 55%
SUPERMAN (GUARDIANS 2 LEGS)
676,085,767 100%
304,238,595 45%
371,847,172 55%
SUPERMAN (GUARDIANS 3 LEGS)
770,127,773 100%
346,557,498 45%
423,570,275 55%
SUPERMAN (AVERAGE LEGS)
781,988,926 100%
351,895,017 45%
430,093,909 55%
GUARDIANS 3 SPLIT
SUPERMAN (GUARDIANS 1 LEGS)
964,021,328 100%
404,888,958 42%
559,132,370 58%
SUPERMAN (GUARDIANS 2 LEGS)
724,377,608 100%
304,238,595 42%
420,139,013 58%
SUPERMAN (GUARDIANS 3 LEGS)
825,136,899 100%
346,557,498 42%
478,579,402 58%
SUPERMAN (AVERAGE LEGS)
837,845,278 100%
351,895,017 42%
485,950,261 58%
Average for all those results is: $809,489,028
So yes I think it can make as much and more than The Batman if the marketing plays its cards right and Gunn makes a film as crowd pleasing and four-quadrant as his Guardians films (which I think he will)