Are the following homebrew feats balanced with the official feats?

Dart Master

• You gain proficiency in darts, if you do not already have proficiency.


• You have a +1 bonus on any attack rolls to throw a dart.


• You can use your darts as melee weapons.


• Your darts crit on 19-20.


• Your darts ignore half cover, get a -2 penalty for 3-quarters cover, and a -5 penalty for full cover.

Reflexive

Twice per short rest, you gain an extra bonus action or an extra reaction on your turn.

Maximized Spell

When you cast any spell, you can choose to do the maximum damage possible, setting all damage dice to their maximum values. However, at the end of your turn you must make a DC 20 Constitution saving throw or suffer one level of exhaustion. You must choose to maximize before you know whether the spell hits.

Precise Spellcasting

Once per day, you can gain a +10 bonus to a spell attack roll. You must decide to gain this bonus before you roll.

Helpful

You can make the Help action as a bonus action.

These are somewhat more overpowered than standard feats

Naturally, in your game, you can hand out whatever feats you wish, but I feel that these are somewhat more powerful, or not in keeping with the design philosophies of 5th edition:

Dart Master: +1 to attack with a certain weapon generally doesn't happen in 5th edition feats. Note that Crossbow Expert and Great Weapon Master don't have this benefit.

Reflexive: The optimal use of this is something like an extra attack or two each combat. Not exceptionally unbalanced, although it would give someone two bonus actions in one turn, which may be uncommonly useful.

Maximized Spell: Dealing maximum damage is exceptionally powerful. This is one of those abilities which is overpowered and balanced by a large penalty, which usually involves the players finding a way to ignore the penalty. In this case, the penalty can be ignored simply by long-resting between combats, which isn't something I'd want to encourage. The saving throw means you will often get maximized effect for no drawback.

Precise Spellcasting: Again, the drawback to this is that it only works once per long rest, which can be circumvented by having more long rests. It also has the attack bonus issue, where 5th edition would rather give Advantage.

Helpful: Giving a new bonus action may encourage characters who rarely use their bonus actions to start using them more readily. Two characters with this feat could easily grant each other permanent Advantage. That combination makes this too powerful.