...For mending, I think a ton of DMs are unintentionally house ruling it. If something is big and broken a lot, Mending isn't supposed to work. It specifies "a single break or tear in an object...as long as the break or tear is no larger than 1 foot in any dimension." It then details the examples for that which match that, "a broken chain link, two halves of a broken key, a torn cloak, or a leaking wineskin."
I think a lot of DMs let you repair anything non-magical that's broken with Mending, repairing one break at a time. But it doesn't do that, as written. I think it's fine DMs houserule it to be more powerful, but out DMs don't.
I'd say you're getting into the realm of DM interpretation rather than DMs are houseruling something. A massive machine that was hit with a catapult can't be repaired by mending - but if you take the pieces of it apart and mend each one, you might be able to fix it.
The spell repairs one break or tear in an object you touch. The
break or tear can be no larger than 1 foot in any dimension. The object can be any size. One example they provide is a cloak - which is much bigger than 1 foot in 2 different dimensions.
The spell does not say you can't repair more than 1 break or tear in an object with subsequent castings - just that you make only one repair per casting and that the repair can be no larger than 1 foot in any dimension.
Let's say the PCs drive their wagon in rough terrain and end up breaking the rim of the wheel and several spokes. One mending spell can't fix the wheel because the damage is in multiple locations, and covers an area greater than 1 foot. However, each spoke might be able to be fixed (if you find all the parts or are missing areas smaller than 1 foot in length) with between one and a few mending spells. Further, if you have the outer rim of the wheel, you can hold the pieces in place and each break can be mended separately as the area to be mended is less than 1 foot in all dimensions.
With this in mind, so long as the maximim 'hole' dimension left in any object does not exceed 1 foot in any dimension, you can repair it. Even when it does, you might be able to repair parts of the damage by repairing 'subobjects' within the larger object (such as repairing the spokes on a wheel before repairing the rim of the wheel) and then be left with a gap that is now smaller than 1 foot.
I fully recognize that a DM might look at what is written and draw a different conclusion - but by RAW, I believe this to be the correct interpretation.