The frequency is already back to the way it was since version 3.120 and earlier, I'm not sure what else to say there. The marauder counter goes up by 1 every 80 seconds, and the counter has to be at least 15 to have any chance (a 4% chance, I think) of spawning, which is checked just after each increment. The chance goes up by 4% with each additional point on the counter, until it's 100% at 40 or higher. Or something like that, I may be off on the actual percents.
Anyway, that means there's a minimum of 15*80 = 1200 seconds = 20 minutes between spawns, and a maximum of 40*80 = 3200 = 53ish minutes. That's on difficulties >= 5 and < 9; diffs < 5 have much more frequent spawns (low cap is 2, high cap is 9) but much smaller, wheras diffs >= 9 have larger but less frequent spawns (low cap 30, high cap 80).
Are you seeing spawns more frequent than that would indicate?
They are supposed to be a significant event, even a major event in some cases. If you find yourself carefully considering whether you want the challenge of enabling them when setting up a game (while still feeling tempted to do so), we've accomplished our goal