The main problem with speccing a game of TF2/OW is the fact that you really can't get the best of both worlds when it comes to observing the raw skill as well as what is actually going on. You can probably get a better understanding if you play a bunch which makes it easier to watch but I said it before the game came out that it will struggle with casual viewers for the exact same reason. In order to truly grasp what's going on, you need to be watching the game in third person as there are a lot of moving parts. However, if you are watching in third person, you don't see how talented the players are at the various things they do (mostly aim which is why fp view is always on fps because people can relate to that). Watching in first person, you get to see how amazing the players are at the various things they do however, it is easy to get lost it what the fuck is actually going on. It's the same way if your team has shit comms but you are still playing well, it's hard to understand what you should actually do.
In Dota, the skill is shown when you watch in third person. There's no first person to really understand the skill of the game. This is why Dota and MOBAs are a good spectating game. CSGO is also a good spectating game because the action is slower and less chaotic. We can watch the CT defending the site where the T are about to approach and have a very good idea of how the game is going. Since the action is concentrated in one or two areas with action being very linear, it's easy to see the skill and the action at the same time.
Luckily for OW, they already have a huge playerbase so they can still comprehend what is going/the skill of the players when watching the opposite viewpoint.