I understand why people are asking why we aren't trying something different set up / formation wise to pick up some better results, but please try to get passed the emotion and consider this logically.
He's been asked to takeover a shit show mid season, that is a fact and is undeniable and very important just for overall context.
He's also been asked to take over because he's been admired by the board (or someone on the board) for the job he's done at Sporting and what he's achieved there. All of this achieved by implementing his methods. And I leave that vague purposefully because his methods include not only playing in a 343 formation, but in the way he operates, the mentality he instills and his ambition.
He's been told we're really struggling for dough (whether that's cashflow, PSR etc) and they will have to be very shrewd in the market going forward to make enhancements to the squad. This is also fact, I'd say so anyway going by the comments he's made multiple times in the media regarding the mistakes made in the past and how they just can't make these mistakes in the market going forward.
So what we know is, we were (are) a shit show, the board want the team to play Amorim's way (I'd like to think most people would be on board with playing the way Sporting were under Amorim?) but that alone doesn't mean too much in the context of this season standalone. We were pretty screwed when he took over anyway so I understand the short sighted view of, lets play a different way to pick up points in the league to an extent (to an extent because our league postion is essentially no mans land anyway - we're not getting relegated and we're not finishing in a european place). And finally, we have pretty significant financial issues.
Where changing formation / style to pick up results becomes problematic though, is the money issue we have. This squad cannot be immediately turned over to suit Amorim's needs, we simply don't have the PSR room and even if we managed to create that room with the sale of guys like Rashford, Garnacho etc. we would still have cashflow issues. Amorim needs to play this way for the remainder of this season because he needs to know who gets it. We're not going into next season with a whole new squad, there will be a decent group of players in our current squad who whether Amorim actually rates them long term or not, will be part of this squad next season and he needs them to be able to play his way. If he came in and abandoned his set up, formation, call it what you will, he'd be entering next season still not knowing if half his squad that he'll need to use could play his way, even worse, who in the squad could actually play his way so they'd have potentially let players leave who may have actually been better suited to his system. Make no mistake, this isn't pure stubborness and arrogance on Amorim's part, there probably is some of that, I'd expect that from a top manager but the squad are on trial here and you can bet your arse he's keeping the ones who are coachable and fit his needs above all else.
Personally, that makes absolute and total sense to me given how his hands are tied financially.