I think the .270 is ok for the job in hand but is limited in bullet (not head) weight options as others have already said. The Naturescot guidance you are quoting is just that, guidance. I think 150gr is not a bad arbitrary minimum weight to quote in the guidance but in .270 I would probably be happier with a 130gr Fox or Barnes NT than a 150gr standard cup and core bullet. In 7mm or .30 options there are some great 150gr bullets for boar such as Accubond, Partition, Swift Scirocco, Fox or TTSX.
You keep referencing the need for a big wound channel. You first need to get your bullet to penetrate a lot of tough material before getting in to the engine room. Therefore bullet construction is key and hence why I would always recommend a stout bullet of bonded core design like the Oryx or Accubond or a slightly lighter NT such as the TTSX. If you are shooting stationary pigs at relatively close range at a feed station then you will be head shooting anyway and any half decent bullet will do that job no drama so long as the operator is capable of good accuracy and understands the behaviour of boar and their anatomy. However, what about the 2nd pig that stops 100 yards away or the one you bump in to walking to the seat? You need a bullet that can cope with the range of shot placements you encounter as a pig hunter and, in my opinion, that means a stout bullet with plenty of energy.
A standard cup and core or SST in .270 150gr will be fine for head shots at feed stations and fine most of the time on most of the pigs in most of the scenarios but you are, in my opinion, increasing the risk of poor outcomes some of the time on bigger animals or with sub-optimal shot placement.
I have shot a couple of them with a .243 55gr ballistic tip but would strongly advise against it. Last one was a decent sized boar and despite perfect head shot placement it was only stunned and required 2 more!
Just my tuppence worth but based upon 20 years of shooting boar in UK scenarios.