Erm, the pitch pine worktop in your first link is not pitch pine- it is pitch pine effect laminate. I have not found any company that provides real pitch pine worktops (that said, I have not searched extensively).
Maybe because nobody has imported much of it since just after WWI due to clear felling of the reserves in Canada and the USA? Between the wars parana pine started to supplant it rapidly. When you see pitch pine today it is invariably recycled, being resawn from beams pulled out of demolished industrial mills - and there is a lot less of it around as most of the mills that could be demolished are now long gone, making pitch pine more expensive than oak. For surfaces in contact with food that immediately gives you a problem - is it contaminated with anything toxic? It is really awful stuff to machine - the name gives it away though,
pitch pine, which translates to it gumming up every piece of machinery which touches it as well as gumming up sanding belts double quick. Think about how much machining and sanding goes into a staved worktop and it becomes obvious why nobody wants to use it for that. So, pitch pine - really good structural timnber but naff all use for furniture and interior fittings, not that I'd expect a designer to understand that fact. The one good use I have seen for it is exterior joinery such as replacement door frames and sash window sills where it's rot-resistant properties can be a major plus, although it can be a so and so to seal and finish
As a decorator, I expect powered based fillers to blow over the years when used on timber, especially on dynamic joints. TBH, any filler will though. MS polymers will offer a decent amount of movement (more than epoxy resin fillers) but they cannot be sanded (or dyed).
As a joiner I invariably use 2-pack fillers where a painted finish is involved, but they generally aren't suitable for clear finishes of any type. I have also done "rustic oak" flooring where to fill the gaps we fixed plywood blanks beneath the holes and then filled them with epoxy resin and a coloured filler, sanded over then clear finished the surface with clear epoxy afterwoods to get the required wear characteristics. Looks impressive, but the problem with doing this is that potential timber movement is a nightmare so the stuff has to be kilned (to match the RH in the building once it is in use, so generally 6 to 8% - far lower than normal, but right for a centrally heated building), checked and installed promptly upon delivery to reduce the possibility of movement (and no wet plastering afterwards!). Done the same to encapsulate coins on a floor in front of a bar in Spain some years back. Looked great, but needed resanding and polishing out every 18 months to 2 years to keep it looking good
