Chess is mostly tactics.

Agree or Disagree?

"Yes, you can easily become a master. All you need to do is some serious, focused work on your play.
That "chess is 99% tactics and blah-blah" thing is crap. Chess is several things (opening, endgame, middlegame strategy, positional play, tactics, psychology, time management...) which should be treated properly as a whole. getting just one element of lay and working exclusively on it is of very doubtful value, and at worst it may well turn out being a waste of time." - IM pfren (August 21,2017)

Agree because all moves is tactics

I agree that the "chess is 99% tactics" thing is crap. It was on my mind as I asked the question wondering why it's crap. So I phrased my question here a bit differently using the word "mostly", aiming at 50.01%. So what percent of chess is tactics then?

@FastLikeAJet How's the first move in chess a tactic?

Tactics are necessary, but not sufficient, for chess mastery. You can't master chess without becoming good at tactics, but tactics alone are not enough to master chess. Also, while one can make academic distinctions between opening theory, tactics, and planning/strategy, both opening theory and endgame strategy are intertwined with tactics. And opening theory and endgame strategies are even connected to each other.

 Disagree. Chess is not mostly tactics. Chess is almost completely tactics - with some minor exception (which are also linked to tactical possibilities or previous experiences).

Let's say one's average at chess but a tactical giant. What percent of those tactical skills would come in handy in an actual game against an opponent of equal rating?

Pfren is right if we talk about chess at the highest level. But for most folks? Chess is:

Inaccurate openings

Poor middlegame play

Terrible positional play

Tactics which are there no matter how good or bad you are

Psychology, if wondering if you should randomly play h3 or h6 to stop your knight from being pinned can be deemed as psychology

Time management because it's a thing

9 times out of 10 I or my opponent win because someone blundered something. King and pawn endings are a rare guest and we manage to blunder in those too.

 Given that rating is a measure of your chess skill over long term, you'd be expected to score ~50% against an opponent of equal rating, regardless of each of your specific strengths and weaknesses. I have no idea what your question about "% of tactical skills coming in handy" means.

Chess can be broken down to 2 parts:

1) executing a tactic when you see it.

2) creating a scenario to get the opportunity for tactics. This is called strategy and/or planning.

To be good at chess, one needs to create and then execute tactics. If you are only good at one or the other, then you won't be good at chess.