What a weirdly ahistorical complaint to make. "You can't have a meaningful campaign with lighter rules." Nonsense. Yikes. What a take. I guess you weren't around in the first decade or two of the hobby.
No, I was. That's part of the reason I have the opinion I do.
Same with AD&D. The only rules you actually need to play AD&D are in the Player's Handbook, which is 128 pages in total.
I think you may be misremembering. All the combat tables and rules are segregated away from the players and placed in the Dungeon Master's guide which I believe comes in at 240 pages. And while technically there might be enough summary of the monsters in the appendix of the DMG to play without the MM, it would not be recommended. So chalk on another 112 pages. As a practical matter, you needed the three "core books" to play the game which runs you 480 pages.
But what's really important for this discussion is that anyone who has played 1e AD&D for any length of time comes to realize that it isn't a complete game. And even the designers were aware of that before 2e came out, which is why they started expanding the game in supplements like the Wilderness Survival Guide and Dungeoneer's Survival Guide.
The way people in the "old days" dealt with the fact that the rules didn't describe a complete game (in all sorts of ways) is that they made a lot of house rules and house rulings. So many in fact that no two tables of 1e AD&D were likely playing the same game. These rulings whether formally written down or not still have to count in the actual page count of the game. And just how problematic this was can be seen by reading modules like C1 Hidden Shrine of Tomoachan and S2 White Plume mountain where so many encounter areas functionally have new rules in their location descriptions, where because the rules were absolutely silent on things like how to handle swimming or how to handle a skill contest the writers invented minigames to handle the situation and recorded the new rules in the encounter. And THOSE also have to be included in the page count of the actual rules of 1e AD&D, and it includes such common things as "roll under your ability score" that wasn't to be found really in the text of the Player's Handbook or the Dungeon Master's Guide but became a very common house rule.
Much of the 1e AD&D DMG just assumes like the text of the B2 Keep on the Borderlands that what is left out can just be created by the DM that is interested in it. It hints and inspires about aspects of the game like dynastic play by giving a price list for a do it yourself castle, without giving a full rules framework for dealing with it. This is why Dragon Magazine was such a fertile ground for rules extensions in the era.
1e AD&D absolutely trended toward the 1000-3000 pages of rules that I suggest are what a game publisher should be shooting for in terms of completeness.
Yes, you absolutely can play campaigns with lighter rules or less/fewer rules. People have for decades without problems.
I can't speak to that. I can only tell you that in every game I've ever been in as a player or DM, the need for rules multiplied the longer the game went on because we kept running off into the blank spaces of the rules much like in early published modules you might run off into the blank spaces of the map with the expectation that the DM would just fix it.
Traveller I'm only familiar with from Mongoose 2e, which I find brilliant, but it's a whole lot closer to what I'd expect in page count than it is to 128 pages. 128 pages might give you a bare bones "Truckers In Space" but I guarantee you that the game wouldn't stay there because I know from retroactive research into earlier editions of Traveller that it didn't. Or if your game ignored that and stayed with the 128 pages, well you got a lot more patience for doing the same thing over and over than I do.