Oh definitely, you are spot on. But very few people actually do. And some things can’t really be adjusted for without changing the recipe beyond what would normally be. A ragu, made properly, means reducing the tomato by a half or even two thirds to concentrate the flavour, and that’s not really possible in a slow cooker. Sure, less tomato to start with and more purée and a bit of anchovy will approximate the flavour, but not consistency. That doesn’t mean it will taste bad, but it won’t taste the same as a ragu made conventionally. Some things will be far easier to modify, and absolutely seasoning is key.
I’m sure every slow cooker user on mumsnet is completely on top of how to adjust seasoning, quantities and ingredients to make the most of a slow cooker, but in my experience these things are used for convenience and so short cuts get taken. I get it - if you are time poor then being able to prepare a hot meal easily so that it’s ready when you get home from school / work is invaluable. But the moment you start searing meat, browning onions, adding ingredients part way through, taking the lid off for the last hour or whatever, then convenience has gone out of the window and you are left with something that would have been better cooked another way.
It does remind me though, that regular ovens also have timers and delayed starts. My mother used to occasionally use the delayed start on the oven for, I think, just reheating a casserole so that it was ready when we got back from wherever we’d been. I suspect nowadays there would be hand wringing about leaving a dish containg meat out of the fridge for 6 or 7 hours though. I have never used the timer on an oven and I’m 54!!