It's from things like properly last hitting creeps, good reaction timing, good reaction decisions, coordinating real time actions with teammates in milliseconds resolution.
It's obviously not about clicking fast, but it is about timing, sometimes 100 milliseconds reaction time make huge difference in outcome. It is usually making decisions on very small time scales. Do you retreat or continue? Use ability or hold it? Can you overextend?
The only meaningful strategic decisions in dota (which you have long time frame of deciding and effect the game for a long duration) are draft (which AI doesn't really master, they reduced the heroes pool to simplify) and item purchases, and there are only a handful of them (~6) in an entire game. Other decisions don't really have a long "memory" time, a minute or two at the most. After two minutes every other decision is just reduced to the relative advantage between the teams.
There used to be one hero in Dota which made it a strategy game instead (techies). But it was like playing a different game and everyone hated it and it was effectively removed. Techies was like playing stratego against chess players, they obviously get pissed off by not playing what they wanted.
There are larger strategic decisions that are significant in dota. Which area of the map to play, which objectives are important and when, what type of fights will we win (fast and bursty) and when will we take them. Often times these are thought of at the beginning of the game and effect gameplay throughout.
That's pretty tactical decisions, usually made in a time window of like 20-30 seconds top. Takes like 40 second to reach more than half the map from the base. Fighting decisions usually also get tactical. I would say that 90% of the game deciding decisions have a time window of less than 30 seconds to make. 70% are in a time window of seconds. You don't make a strategic decision to fight ever, you make tactical decision when the map looks fitting. If you take strategic fights because of long term strategy (instead of deciding tactically) in Dota you will lose.
I feel that I generally know where I will play well in advance. Like before the game starts. At this point it just seems like semantics of what we think of strategy vs tactics if that's the case. As I think many of the things you see opportunistically while I decide I know when I'm going to fight in advance and I put myself in opportunistic positions at those times.
in dota the tactics is to do with the execution of abilities, often times in coordination with other agents in execution of their abilities to get combo effects while adapting to the situation as it unravels.
As an avid dota player I wouldn't agree with your characterization that 70% of dota 2 is your definition of tactics. What I've noticed differentiates player MMR the most is the strategy applied to each context. It's rarely the execution that's the problem as you can gain such overwhelming advantages through strategy.
There's barely any long term strategy in Dota, only meaningful strategic decisions are items and heroes. Even ultimate usage has like 2 minute window of importance. Wards too. And maybe the decision to push high ground because of how many times games are lost because of it, but it's the tactical errors usually making most of the difference there.
I'm immortal (6k MMR) and agree with the parent. I used to think similarly as you, because my mechanics were very good, but as I started to play with friends who are much lower ranked, I noticed that they can often execute things (e.g. ability usage) pretty well, but their overall play and strategy is desperately lacking. Things like playing the wrong areas of the map, spending their time inefficiently, never capitalizing on their strategic opportunities (e.g. not playing where they have vision, not playing in areas of the map that are near their objectives, not taking calculated risks based on available information).
I do think OpenAI five derived some of their advantage from seamless ability usage, and inhuman coordination in lane, but it also did some novel things strategically, that challenged some of the established tenets of high level play (e.g. they had a lot of mobility on the map, back when that was considered very inefficient).
Like is it just the speed of your clicking? Or is it more than that, like the most basic kinds of strategic decisons?