There are many who say that MDF dulls cutting tools very quickly. But I do not think it does compared to many woods. I would think even pine is a harder material than MDF. How fast can it dull tools? Or does it do other wonders to a cutting tool because of the glue, like jamming it up?
The glue is much harder than the wood, hence the extra wear on blades and tools. Pine is pretty soft compared to hardwoods, but construction lumber is often wet which might explain your experience with it in that it can gum up equipment faster than well dried hardwood.
How fast can it dull
It depends on the quality of the blade. A high quality blade will last longer than a low quality blade.
There are many who say that MDF dulls cutting tools really fast.
Bear in mind that a lot of that is from people milling it with power tools, where the blades are moving very quickly.
But I do not think it does compared to many woods, even pine I wold think is a harder material than MDF.
Well there's pine and there's pine, there are many subspecies and a lot of variation between them. But broadly speaking I think you're right.
In fact I find MDF is not particularly dulling to tool edges (with hand tools).
Compared to other board materials, chipboard/particleboard in particular, it's like cheese! While the glue used in chipboard can be the same as that used in MDF but it's not finely spread though the matrix of the material as it is in MDF and as a result the cutting edge contacts actual chunks of glue. Just from a few experienced working it with hand tools chipboard seems to be perhaps >20 times more abrasive O_O
And of course there are a great many tough or hard hardwoods that would be far above MDF which is soft enough to easily dent with a fingernail. Some hardwoods are merely much harder, e.g. purpleheart, African blackwood, but a few woods (commonly tropical hardwoods) contain silica and this makes them notorious for quickly dulling cutting edges, e.g. teak.
How fast can it dull?
I think this is a "How long is a piece of string?" kind of thing.
How wearing any material is to cutting edges depends on many factors, the quality of the steel probably being the most critical. Note: not just the steel alloy itself but how it's hardened. It's not at all difficult to start with a good, even excellent, steel and end up with a mediocre blade because it wasn't hardened properly. This is not an uncommon issue with low-end chisels for example where the steel may not actually be poor as usually stated (it would commonly be a perfectly reasonable high-carbon tool steel) it's just poorly heat treated.
Edge geometry is also important, the shallower the bevel the greater the tendency towards blunting. For a chisel a shallower angle would make it much more effective at slicing through wood, so there's a tradeoff. With most plane blades though the included angle on the edge is much less critical to performance (a 10-12° difference can be barely noticeable) so you can hone specifically to make the edge more durable if needed without a significant hit in planing resistance.