As you said, F3 is somewhat alike Indycar so I think we should watch F3 with the expectation that we'll get to see almost the same-like cars and almost same-skilled drivers.
But one thing is that since the cars are almost the same, drivers get a chance to showcase their raw driving talent and that's something that I enjoy.
Cars could be worse, teams could be worse, drivers could be worse, but not having any type of dynamic or adrenaline rush is the lacking part. I watch F1 and have fun because it is such a fast paced adrenaline rush, anything could happen at any moment, but here? It just feel like cars going around and finishing without much happening in between.
I think not having better cars and drivers is directly related to the level of entertainment they can provide.
For example, in F1 we have better drivers and better cars, and also better marketing, so the hype is always there.
But F3 doesn't market that much as F1 or neither do they have the quality drivers. As a result, the hype is not there, and watching F3 for us F1 fans seems bland.