While in principle that makes a lot of sense and is something I definitely aspire to incorporate in my DMing, in practice... in practice there are many instances in D&D where single PC / single skill check resolution is exactly what's called for (or at least is what has traditionally been called for in D&D's history).
How do you handle situations like a rogue picking a locked door or a locked treasure chest? These activities have, at least since AD&D if I remember right, been things that involved skill checks in some form. They're not necessarily "throw away checks" either, because there can be interesting consequences for failure: enemies hearing you, a poison needle, breaking a lock pick, etc.
Do you hand wave such instances with auto-success (i.e. "you fiddle with the lock and eventually slide your pick into the tumbler teeth until you hear that satisfying click...because that's what rogues do")? Or do you make every locked door or treasure chest in your game a skill challenge?
On a more meta level, combat has more tension and more decision points than opening a locked door or a locked chest. 30 minutes for a combat? We don't blink. 30 minutes to open a locked door or chest? That would be supremely aggravating! Of course, if it's a Stargate-like device opening a portal to the Lower Planes, well, then that has more narrative weight and certainly could involve multiple action steps & decision points... But sometimes a locked door or chest just makes sense, right? Rolf the butcher may not have a portal to the Abyss in his backroom, but he just may have a chest with confidential letters proving he's a spy for the cult, and perhaps a self-igniting mechanism to torch the evidence if the chest is improperly opened.
In my games DC has a rationale and consistency - so the Dc is pretty much easily determined.
So a character picking a treasure chest or door lock might be seeing a 10, 15 or 20 in most cases - varying by what in essense biols down to skill of the maker. Some times that may adjust to 25 or down depending on assets, diligence, upkeep etc. etc.
Notice the level of the rogue, the fact that they have guidance etc do not apply to the DC.
So, it may well be that the rogue can easily beat the Dc20 especially if they are at reliable talent and have expertise on it. Thats a factor of the character ability and its not my job as Gm to change things up so that those checks always pose a challenge.
if its appropriate perhaps magical locks or runes to explode etc can be there.
So if they apply guidance - great - after all its someone calling on divine blessing - not providing their own skill. No roleplay needed - just cast it- thats what its for.
As for "working together" i have no problem with say working together to disarm a trap but probably most of the time working together on a lock might be difficult - just depends on the lock type and scenery. Really hard to get four hands to pick a normal lock - but if its say a safe lock - could be two sets of ears on the door listening for tumblers.
But i suppose at your core question - yeah - if the guidance and working together defeta the DC thats great in my book. its player characters using abilities to overcome a challenge.
The key thing is from my perspective as GM i *know* thats the case so i do not get heavily invested in a skill challenge thats as simple as one roll being a task that tasks the PCs.
After all, that chest lock - one knock spell.
That "hard to work together" - one Enhance ability lasts for an hour.
That foraging check - one goodberry feeds ten people for a day.
There are a ton of easy magical solutions for many of these "skill tasks" if the task is simple and a single roll without any complicating factors.
If i worked and reworked DCs time and time again to make these checks always a "challenge" not only am i nerfing the character growth (tier 1 vs tier 2 is pretty solid hallmarked by easily dealing with simpler tasks) but i am simply pushing them to not bother with those and instead work it with magics.
That said, if i wanted to make them challenging i can indeed rule the lock is a particularly complex one - multiple locking mechanisms and turn it into a trio save system - but again, unlikely for most cases.
maybe that answers your question but i think we have a fundamental difference on not just how to but whether or not skill tests should be a "threat" to a party at different levels and times. your poison needle trap chest could be a nice challenge for say 1st-4th level rogues - well - unless the wizard or arcane trickster uses mage hand to open it.