I mostly agree, but I think there's a work around that slipped my mind during this session. The 5E text of mage hand specifies the hand can't carry more than 10 lbs which I think could be interpreted to mean the hand can't exert more than 10 lbs of force. A quick Google of force required to open a stoppered bottle indicates 49 to 85 pounds of force, so I think it would have been fair play on my part to inform the players the hand was unsuccessful in opening the jar, imagining a tight fitting clay stopper is keeping it shut. I think paying attention to this sort of thing might help curb use of mage hand in the future which until now has played a part in the resolution of every trick/trap encountered in this adventure.
I don't think getting that pedantic will help.
Mage Hand is a bit of a shortcut for ye olde days of 10' poles, tongs, heavy leather gloves, ear cones and the like that were mechanical equivalents for defeating traps and the like.
These traps are generally just a tool to reinforce that there's no free lunches - anything that looks too good or easy is, in truth, a trap. There's a bit of a puzzle to get at the goodies, but its a puzzle that once solved, the party will just develop a standard operating procedure for getting the goodies. Unless you want to get tied into a race where you have to come up with a new and different way to defeat every trap encountered (and the party has to play "how do we outthink the DM"), things will just get more convoluted.
I don't mean give up on traps, but if
Mage Hand is a problem, this sort of passive-aggressive approach isn't going to fix the issue. Be forward with the issue and straightforward with the fix. "
Mage Hand can't open stuck containers or doors - or requires a spell attack vs. a DC to open such portals/containers" would be more straightforward, and then you can define what is "stuck" without going down a pseudoscientific route of specificity. The spell is still useful and still works for what it was intended for, but less of a cure-all and most of all, doesn't automatically succeed. Another route might be to increase the casting time for
Mage Hand - especially effective if making wandering Monster checks - so that it is employed less often or for more dramatic times. In many ways, I wish cantrips had never been made at will, and a limited number of uses per day might lessen some of the hassle they cause (both
Mage Hand and
Guidance).