It doesn't seem like you disagree completely. You said the game isn't challenging enough. I was saying "challenge yourself". That's not disagreeing completely..we're saying 2 different things

Challenge yourself if the game isn't challenging enough, or quit playing it and play something that is. I gave only a couple of examples how someone could challenge themselves. Do it any way you can think of.

Well, we agree that there is a sandbox aspect to the game, but we disagree about what should be done about challenge, or the lack thereof. It's the developers' responsibility to make sure the game presents a challenge, not the players'.
Imagine if there were a chess game on the market whose AI was so poor that you had to essentially handicap yourself in order to have a challenge. Would that not seem utterly absurd? It might have been one thing back in 1980 or something when possibly the average desktop computer would have been hard-pressed to have the processing power to run a really smart chess AI, but nowadays, it would be inexcusable, and nobody would play it. Skyrim's problems aren't nearly so extreme, but apparently there are aspects of the game that are not properly balanced - in other words, the player has to handicap themselves by not doing certain things and not trying as hard as possible to win, in order for the game to retain a challenge.
And lest somebody get their panties in a bunch about my use of the word
win, yes, I know, there's no end to the game where you "win" and take the princess home to Toadstool Castle or whatever. You certainly "win" whatever little challenges you set yourself, however, like clearing out a bandit stronghold or leading one side or the other to victory in the civil war, or whatever. If you win those things too easily, then the game's level of challenge is out of kilter for you and you need to raise the difficulty level. If you raise it to Master and these challenges still present no - well, no
challenge, then the developers need to rebalance whatever it is that made it too easy.
And it sounds like there's a very strong argument to be made that some skills and perks need some re-evaluation, surely. From what many, many people have said, either smithing, alchemy or enchanting, or the three in concert, are simply too powerful and need rebalancing. Whether that rebalancing takes the form of weakening the effects of one or all three of the skills, or whether it takes the form of simply reducing the rate at which you level those skills, something likely needs to be done. Ditto for some of the sneak perks; when people talk about leather-clad thieves one-shotting giants and ancient dragons on Master difficulty with no smithing, enchanting or poisons involved, either they're full of prime-grade organic fertilizer or else, again, the developers need to do some re-evaluation of the relevant perks.
As I say, I understand the toy aspects (or "sandbox" aspects, if you prefer) that are certainly part of Skyrim, and they're part of the undeniably awesome appeal of the game. But let's not forget the
game aspects to the game, shall we?