To be doubly fair, the game has always been envisioned as a progression but the progression has always been able to be easily circumvented and rushed by those who wanted to do that. It still can be circumvented and rushed but you will have to do it by blatantly enabling the creative mode rather than exploiting the loopholes that once allowed people to rush the progression. The game can still be played as a pure sandbox but that is going to be increasingly through the use of creative mode.
Remember that just because you use creative mode, it doesn't mean you have to fully use it for everything. Someone like me enjoys using a wood base for the first bloodmoon and then a cobblestone base for the next two to three, and then a concrete base and finally a steel base for the higher bloodmoons. So I probably would never enable the creative mode since the amount of mining I need to do in the beginning is minimal. By time I'm going for concrete it is around day 30 and I've progressed to the point where I'm ready-- and (IMO) getting a concrete base for the first few bloodmoons is totally overkill defense-wise and makes them so boring (for me).
Someone like you who enjoys mining but only with the best tools and wants to get to concrete as early as possible and is probably going for a much more massive build than I might use the creative menu only for getting those tools and that it.
Then there is sure to be someone who hates mining in any form and they just want the blocks. They can open the creative menu and take 20,000 concrete blocks out and get to building without going through the grind of mining and crafting those blocks.
In single player I don't see any harm in using the creative mode as much or as little as you wish in order to make the game a fun sandbox experience. In this way those that want a progression to the game can do that and those that want less rules and more sandbox can option in the creative mode to get that. In fact, if it was my game I would re-label "Creative Mode" in the options to "Sandbox Mode". That would remove any doubt about what option to toggle in order to get the full sandbox gameplay back into the game.
Truth be told, I pretty much always have the creative menu enabled. I've only used it once or twice (there was a CompoPack POI I like and wanted to live in, but it had an unavoidable booby trap that would blow up a bunch of blocks, so I used creative to repair it, which was mostly for aesthetic reasons), but I'm 95% of the time playing modded, and it's just a habit from years of playing modded Minecraft to have "cheats" enabled to fix things when they inevitably break. Strangely, things almost never break in 7 Days unless they're broken from the beginning, or I do something silly like try to remove a mod.
That said, if I tried to use a wooden base for Day 7, I'd be in real trouble, because my Day 7 hordes generally include cops.
I generally don't get (self-produced) concrete until Day 14, though, and non-critical parts of my base may not get upgraded just because of time. Some of the mods I use generally necessitate concrete by Day 14, because lots of zombies that will tear though cobble like tissue paper kinda requires concrete.
But yes, I quite often make massive bases (my biggest one was slightly bigger than the max sized 71 X 71 claim area) so I go through lots of materials (I had one playthrough back in A17, iirc, where I had over 2 million clay stuck in boxes because I'd gotten so much mining sand in the desert.) The fact that I hate the auger (it's too easy to accidentally hit a block, and you can't repair ores...yes, I have issues) generally increases the time it takes for me to mine things too.
That said, I don't need the "best" tools (like I said, I almost never use the auger, and I have no problems with lower level wrenches, etc.), I just want tools that don't make me feel like I'm wasting my time trying to mine. Perhaps if there was a stone-tier pickaxe (or the scrap tier that's fairly common in mods was available in the vanilla game or a standalone mod, which it doesn't seem to be any longer) I wouldn't have such issues with tool (and workbench, to be fair. In A20 I usually have one workbench that's just permanently making cobble) availability.
I have no problem modding, so there's likely to be mods to fix any of my expected A21 issues relatively quickly (I've only done some super basic mods of my own.) I'm just a bit sad to see the vanilla game seemingly moving further and further away from what I'd thought for years it was intended to be.
