While I completely agree that the rules should be arbitrated by a DM - and this is one of the many examples of rules I'd feel quite happy imposing another interpretation on - if you're a two-weapon fighter, why do you need a feat to draw both weapons at once? That feat - as well as the object interaction rules (PHB 190) - point to the "only one weapon drawn each turn" rule. The ammunition property also works toward that interpretation; you need something to get around the basic rule.
Cheers!
I don't see the sentence in the ammunition property as being a positive prohibition from thrown weapons without that property combining a draw and attack. The design of 5e places great discretion in the hands of the DM, and both that sentence and the list of object interactions read to me as guides to DMs to allow those actions without forcing players to use their actions for relative minutia. IOW, I see them as indications that the drawing and throwing of javelins (and other thrown weapons such as daggers) should be part of the attack, not as a limit.
As for the dual wielder feat, the weapon drawing aspect is there, by my read, because there will be many dual-wielders who don't have Extra Attacks. Rogues, for example. Fighters and Rangers before 5th level. The feat allows them to be good to go with just their regular attack and bonus action attack. But a character with Extra Attacks should, by my read, be able to draw a weapon and attack with it on each attack.
For example, let us assume we have a TWF Fighter, 5th level, without Dual Wielder. They start combat with both light weapons sheathed. On their turn they use part of their move 15 feet to one enemy and attack with one light weapon. Then they move 15 feet to another enemy and attack again. At this point, should they be able to use their bonus action attack? I think yes.
Let's look at a 11th level fighter, without TWF or Dual Wielder. They have a regular longsword and a silver dagger. They start combat with both light weapons sheathed. On their turn they move 10 feet to one enemy and attack with their longsword. For their next attack they move 10 feet to another enemy and again attack with their longsword. On their third attack they move 10 feet to a lycanthrope enemy, and drop their longsword and attack with the silver dagger. Possible? I think yes.
I think both of these examples are corner cases, because generally melee weapons don't require the amount of drawing one sees in thrown weapons. And I think there's enough ambiguity in the rules that DMs could rule in a number of ways; very loose for a more cinematic game, very tight for a more realistic game. But I don't think the rules positively prohibit the above to the degree that we're talking houserules.
