Well... Or they could have created a new type of action...
Something like "free actions" you can do, as regular and bonus actions only once per turn (to switch your weapons, to click a button or a lever, to drop an item on the ground,...).
Oh wait, that's exactly what Tactical Adventure did in Solasta and it works really well ! (Ofc TA has more respect and faith in the source material than Larian).
That depends on how strict you want to be with 5e rules. Free action allows you to interact with ONE item, so switching a weapon is TWO free actions, or ONE free action plus a main action.
Some 5e players say that dropping your existing weapon doesn't require any form of action, so you can switch weapons with ONE free action if you drop your existing weapon. That is certainly resaonable, since ( like disarm ) you then lose access to your dropped weapon, creating a negative consequence. Other 5e players simply decide that the actual 5e free action rule is lame for weapon switching, and allow weapon switching as a free action.
I didn't buy Solasta, as I found the demo level uninteresting, but according to your post, even Tactical Adventures deviate from 5e rules when they think it works better for their relatively narrow audience. Larian have to decide what is best for the much broader audience they attract.
I don't personally care if they choose to keep their existing mechanism, but I suspect it would be a better experience if the number of "ready" weapons you can have reflects your weapon familiarity, and a single weapon switch is allowed per turn. The Solasta model does not sound like an improvement at all.
