Uh, you already have that. It was called swift actions, free actions, ready actions, and standard actions. You also had different bonuses and penalties, but they were made using numbers, not a mish-mash for everything called advantage/disadvantage that does not stack.
Shield bash and charge do exist, but those require a feat that you have to take and let me remember you that in 5e you have to choose between a feat and improve your stats, and you do not have feats until level 4 (unless you play a variant human, which is banned by many DMs).
Most combat maneuvers are now pointless. Knocking someone down only takes away half of their movement, so he can get up, move and attack as always; and stand up does not provoke attacks of opportunity. You can also cast spells surrounded by enemies without provoking. You can disarm someone and he just takes the weapon from the ground in the next turn and attacks without penalties. Flanking is now optional, and some DM´s do not use it. Heavy armour is only useful for a character that has negative dexterity, etc
Those are only a few examples you named before.
5e it´s fun to play, but the mechanics are too simplified for my taste. What I meant by simplified is that they took away lots of features just not to "complicate" things. I usually homebrew some of this stuff just to get back some of them.
I have not played a 5E game yet, but from reading the PHB I like it more than 3E.
I have played played lots of computer RPGs and I think DnD 3E was the ruleset that was most difficult to understand.
I will use Pathfinder Kingmaker as example, since I consider pathfinder as DnD 3.75 and it was relatively close to the PnP rules, as far as I understand them.
I had problems in this game and often my head was smoking when I tried to understand stuff.
The char I made was not good even though I did lots of reading before.
- You have free actions, swift actions, standart actions, full round actions, move actions and maybe more. It was not always clear to me what I can do.
In 5E each round I can move x feet and I have one action, one bonus action and one reaction.
- Stacking bonusses was not easy. For every buff you had to remember if it is a morale, luck, enhancement, sacred, profane, . . . or whatever bonus. Buffs of a different type stack, buffs of the same type only apply the strongest effect. Some stuff from equipment does not stack with spells. I had to write down which spells work together with which other spells or which equipment. Stacking buffs is needed, combat is very hard without. I am sure I was not as efficient as I could have been because some of my spells got suppressed or I did not use others which would have worked but I thought they don´t.
- Same thing for armor. There are many kinds of armor (dodge, deflection, natural, armor, enhancement, dex bonus, . . .), I guess except dodge nothing stacks with itself, some of those worked not against touch attacks or when flat footed. Having a warrior in heavy armor and a huge shield was often useless when enemies used touch attacks. Looks like the best way to avoid being hit is to be naked, collect defensive bonusses from different classes and having wizard buffs. I am still not sure how to be a good tank, most enemies hit me most of the time.
- Personally I prefer the 5E idea behind classes. You start with a base class and then you specialize into a subclass of this class. For me this looks better than the prestigue classes of 3E or adding tons of new classes that are a mix of 2 other classes. In 3E sometimes you had to select useless feats or skills only to qualify for a specific class.
I admit that the system of D:OS2 was too simple for me, though my main reason why I disliked it were inflating numbers and I get flooded with completely random items.
I am not against complexity, but it makes no sense to make things complicated just for the sake of being complicated. No, DnD was never a realistic simulation of anything and will never be.
I have studies physics engineering and one main rule for constructing things was: " As simple as possible, as complex as needed. "
RPGs are one of the most complex type of games and thats one of the reasons why we like them, but the devs should not try to deliberately confuse players with complicated rules.
The character system I like most is the one from PoE2. The basics are easy to understand ( hit chance = acc - defense +1d100, passive effects stack, active effects do not stack ), you have lots of options and the forum is full of different builds and discussions how to make a better char. Only the double inversion ruins an intuitive understanding of most rules. ( The devs have made up a system where the numbers are hard to understand if you combine bonusses and penalties. So a bonus of +20% and a penalty of -20% will not result in zero effect. The system is fine from a mathematical point of view, but players and even some devs have problems to understand it.)