If you go strickly by the rules you are wrong. That is why you can enter in a room and say:"Hey! An invisible magical longsword is in that room. How do I know? It did not take the hide action so it is not hidden and I perfectly know where it is. The PHB says so..."
Longswords dont (and cant) take the Hide action.
When your argument is based in absurdity to make sense, this should give you some indication of how wrong you are.
An invisible longsword in a room has a Search/ Perception DC assigned by the DM, just like a trap or any other hard to locate/ percieve object in the game.
Now sarcasm off. Of course the hidden rule is relatively simple to understand and I believe that we all do but it does not make logical sense.
Yes, it does. As long as you remember combat is simultaneous and work with the assumption that creatures rely on more than just direct visual observation of a creature to detect where it is.
Smell (how often do your PCs shower anyway?), sound (all that armor and weapons and components and other junk jangling around), external visual disturbances and signs of passage (footprints in carpet, grass, mud or dirt, swirling debris and smoke or fog as you move or giant gaping holes in them as you stand there, creaking floorboards, branches being pushed back, doors opening and closing etc etc), touch (youre hiding in combat and likely trading blows/ parrying attacks that get close to you and not standing there like a grinning idiot, knocking away attacks, brushing up against people etc) and other senses are all equally valid.
It makes far more sense to allow wild swings in an invisible creatures general direction (i.e. at disadvantage) when that invisible creature has made no other efforts to conceal itself (moving silently, muffling and concealing traces of its passage, staying downwind etc).
Even then, after casting invisiblity (assuming it takes your action and you also lack the ability to Hide as a bonus action) there is only a second or so in a window of opportunity to make such a wild attack (at disadvantage) before the invisible creature can try to Hide on its next turn. And even if it fails, it can retry the next round. And the next. And the next. And so on.
If I go straight by the rules, an opponent using improved invisibility in a silenced zone will be steadily attacked (with disadvantage) by his ennemy simply because he did not use the hide action.
Exactly. So take the bloody Hide action like anyone else that cant be seen (like those in total cover or heavy obscurement or simply in a creatures blind spot subject to DM fiat for the latter).
Its not my fault if your Wizard dumped Dex and never got proficiency in Stealth. Hes a clutz who makes a lot of noise and isnt switched on enough to cover his tracks, stay downwind of his targets or muffle those darn jangling components as we loudly stumbles around.
In any other system if I were the enemy of the invisible wizard, I would be toast but in 5ed, by strict use of the rule, I'll just have disadvantage to hit.
Blame the Wizard for not making any effort (the Hide action) to conceal himself. His footprints in the carpet, heavy breathing, jangling of his spell components, brushing up against you as he moves around, the smell of his sweat and grime and spell components give him away. He's making zero effort to conceal any of these by not taking the Hide action.
He may be unseen, but he's not unheard (or impercieveable). Remember Hidden is both unseen AND unheard (and not giving away any other signs of your passage). Untill he takes the Hide action, he is only unseen. The game assumes that other signs of his passage (mainly noise, but also scent, footprints in the dust/ dirt/ carpet/ mud, a human sized shillouette in the smoke of the lantern and the ebbying smoke swirling around him etc) are detectable by an alert opponent unless and untiill he takes the Hide action.
When a rule is badly written, you have to use your logic.
Its not badly written. You're just using bad logic and a weak imagination.