If habitat is the limiting factor (IOW there are plenty of young fish born but nowhere for them to occupy and they subsequently die), then you aren’t really helping at all by removing young fish to make way for other young fish. You can’t grow a population if there’s not enough habitat to support them; kind of like continually evicting residents from an apartment building to make room for new tenants; you still only have X-number of units to occupy.
Size and bag limits are heavily influenced by harvest pressure; in the case of this species harvest seems to be mainly driven by angling pressure by people (the linked PDF describes over 1.5 million fish harvested annually). When you have high enough angling pressure you start to impact the age structure of a population, and you can get into trouble if you influence it the wrong way (even if you leave high overall numbers).
Managers need to have specific goals as to how they want to manage the populations; there’s not “1 right answer” as to management. There are different types of fisheries and they are not all compatible with each other; two general types are trophy fisheries and harvest fisheries. Generally speaking, you can manage for big fish or abundant fish, but you can’t have both at the same time.
If your goal is to have a trophy fishery (abundant large fish), you generally have to have very low (or no) harvest, and as little angling pressure as possible - since even C&R angling removes some fish via hooking mortality. If you want a harvest fishery (to fill your freezer with), you’ll need to protect your up and coming young fish until they can spawn a time or two. Harvest fisheries (with a few exceptions) will usually not be able to produce many big fish.
Maximum size limits would target young fish for harvest, and if angling pressure is high enough (as it sounds like it could be approaching for these types of species), you can end up in a situation where the majority of young fish are taken out and not enough of them survive to become large fish. Also, you’ll still be impacting the large fish by hooking mortality even if you release them. Minimum size limits are set to allow fish to spawn at least once, maybe more before they are targeted. You don’t need trophy sized fish to sustain a population, but you do need minimum recruitment and taking out your next generation can very risky from a management perspective.
No, size limits are not bad science nor is C&R a joke. Mortality from C&R angling varies by species, environmental conditions, and experience of the angler. For fresh water lotic and lentic species I work with it’s generally predicted to be about 5%, plus or minus 2-3%.
It heavily depends upon the amount of angling pressure the area/s experience. If angling pressures are low enough you can keep them open and still maintain sustainable fish populations. If you have very high angling pressure however, closing certain areas doesn’t help much because that angling pressure will simply shift 5 miles down the coast and decimate the fish in open areas.
There are numerous books, modeling systems, and decades of research on fish population management, and more is known than people realize. A difficulty however is that most of the people who talk about the topic don’t understand how it’s actually done nor seek that knowledge out, and subsequently spread a lot of bad information based on their assumptions.