As others have said, not having switches means:
A) your house may not be to code
B) your house will be difficult to resell
C) your lights won’t work if your central controller goes down
If you like smart bulbs and tablets, great: leave dumb switches and put switch locks on them. If you’re doing a custom build out, you can even put the tablets on a case mount with the dumb switches inside the case. So they’re there for your Plan B, but aesthetically they’re invisible.
I used to strongly prefer smart switches. However, now that I have voice control with Amazon echo, I’m really happy with smart bulbs and have added a lot of them to the house. At this point, voice is the main way we control all our lights, and it’s rare for anyone, even a guest, to even walk near the wall switch. So it pretty much eliminated the problem of people turning off the wall switch. We can also use voice groups for all kinds of purposes. I have a “bedtime” group that lights a path from the livingroom to my room.
I do really like wall mount tablets, but they tend to not work well for little kids and for people who do not easily read the language the tablet displays in. This might be older people who need reading glasses, or people who speak a different language.
I have a number of health aides who work in my house every month, and the voice control with Amazon works great, everybody likes it. I’m not sure that would be true of the tablet. Anyway, I think the tablets are a great idea. But I don’t think they make switches completely irrelevant.
Specifically with regard to smartthings, it’s just not reliable enough yet to turn over all light functions to it if you don’t have a Plan B.