That logically doesn't make sense though, because it's assuming the same amount of "step it up" (AKA 'progress'), which is not guaranteed. Fusion realized can far outstrip consumables, "winning the race" as it were, even if it takes longer to do so.

This is the problem of induction again. Yes, fusion could have a breakthrough and then really take off. So could other technologies. The question is how likely are these things to happen? So far it's not looking too great for fusion being special in that way.

Well, it hasn't been invented yet. I think we should probably all wait until it actually has, before passing judgment on it.

I'm not passing judgment for the very reason it doesn't exist. I'm making a speculation of what the end point will be based on how things have been going. The fact that it still doesn't exist is a point against the technology btw.

Overall, I sense a general agenda from you, based on your comments, that you wish to forgo the investment in research and development for fusion, and instead concentrate on renewals like a solar, etc.

?? If you're reading my other comments you'd see I literally explicitly say that fusion is still worth pursuing, even if it can't be an energy source... Furthering science is good, even if it fails to do what we might've been trying to do. There's essentially always other benefits that are often unforeseen at the time.

So, to recap:

I think we'll crack fusion.
I think we'll also get better at other stuff at the same time (and maybe find new things too).
I also think that after all that, man made fusion as a source of energy isn't likely to end up on top.
Lastly, (and perhaps most importantly) I think it's still worth trying to get fusion to work because it'd be great if it did! We'll still learn things that can be applied elsewhere even if it's not a great energy source.