(I am concerned that this is polluting the thread with an off-topic discussion that has led to some real consequences elsewhere)
If you argue that providing the switch version provide additional revenue that can then be spent on the core game; the same can be said for adding a different mode of play. By adding that different mode you in theory increase the number of purchases which ….
I don't think your argument really holds up very well because it is hard to find a direct comparison.
If you take a game that was built from the ground up for cross-platform portability and pay someone to make a version for a fourth platform a few years after the initial release, the impact of costs to the company is small, and the amount of money added back into that actual game is basically zero (because it is an old game). Direct comparison - how much money did the Switch version of Jedi Knight II add to the budget for patches/improvements to all version of Jedi Knight II ... easy answer - zero.
The sales of the Switch version of Witcher 3 allow CDPR more freedom to invest in their current and future products, NOT Witcher 3.
I have gotten a survey from the Nintendo shop based on my purchase of Witcher 3, and one thing they specifically asked was about if I already had owned Witcher 3 and on which platforms.
CDPR/Nintendo likely discovered what I have found on forums where you can talk about playing PC-centric games on Switch without getting treated like shit, and that is that MANY people who are playing Witcher 3 on Switch have already played the game on PC or console. That is not new - the Switch, after its initial burst of Nintendo typical sales, has become a great handheld game system that crosses platform appeal.
So they are tapping further into that with the new cross-save compatibility ... they needed a patch, had been talking about it for months, so it was awesome that they chose cross saves.
But let's not over-estimate what is involved ... cross saves involves making the save game reveal its source, and having the game be able to ignore things the current platform can't do but not change any of those things, so that when you go back you can retain the original experience. The fact that the new patch has more graphics adjustment options has already led to some glitches, not surprising, but nothing big.
Combat gameplay is at the very core of a game - making changes there impacts EVERYTHING, and so those types of changes can be incredibly expensive - and has to come from the core game development team, and requires heavy amounts of time-intensive testing. That is all just a simple reality.
HOWEVER determining which players purchased the game due to a new feature (like cross save compatibility) is equally hard.
Cross-saves I look at as 'grease' - they help push the sale of something that someone was already likely to buy. The Witcher 3 has seen an incredible bump in sales due to the TV show, and the Switch version landed at the perfect moment to be one of the biggest sellers last year on the platform, and also sold systems to gamers. SO it is a special case.
I will be honest - I have been playing RPG on a computer for ~40 years, been involved in
'forums' on USENET prior to web and social media ... and while there were some debates around the time of the original Baldur's Gate, I have NEVER seen this sort of 'religious war' around turn-based vs. RTwP that has gone on specific to this otherwise decently well behaved forum and just recently. Never.
I mean, specifically - here we are in a thread about the Switch port of a real-time action-RPG getting new features unrelated to gameplay ... and you have chosen this as another front in your holy battle? This is not normal. This is not happening elsewhere ... this is truly a very small group of people on what they see as some great crusade. And I use 'crusade' because it is not a 'war', because one side is pretty much cool with either (despite preferences) while the other is "give me turn-based or give me death" along with "if you are not with me, you are my enemy"
How many copies of a game - an isometric, party based 'classic' RPG - would be sold/not sold specifically due to whether the combat engine is turn-based vs. RTwP? 10? 20? Perhaps even 25? I honestly doubt many more than that.