I-75 doesn't bend west until you get south of Findlay. From Findlay to Carey (where 15 meets 23) is less than 20 miles. From Toledo directly to Carey is over 50 miles.
You don't even need to go near to Lima. (I-75 doesn't bend west to get to Lima, it bends west to eventually get to Cincinnati.)
Or are you thinking that you have to stay on an Interstate to get from Toledo to Columbus, so you go all the way down to Dayton?
I may not have expressed it well, but my point is that I-75 to either I-70 or US 33 into Columbus is not workable because of that 25 mi swing to the west. If not for that 25 mile swing to the west, US 33 would be perfect as a route into Columbus.
US 23 is fine as a route from Findlay to Delaware, but that last segment is problematic both because of public opposition and it seems like that would be a lot of expensive land to acquire. Now if I were somebody in a position of power, I would ignore the public opposition. They will thank you 30 years from now because gridlock serves nobody well.
If US 23 can't happen, it seems like a four-lane highway between following US 68 and Ohio 31 all the way into Marysville would be a good route. Also can serve as a second way to feed traffic into US 30 into Fort Wayne and Chicago. It's 60 miles worth of freeway though.
Another option is building some kind of a highway between Indian lake and Bluffton which is about 30 miles worth of road, but that adds 15 miles to the trip to Columbus. I don't think that's horrible in the whole scheme of things, but I can see in the whole big picture that might not be very efficient when thinking of thousands of cars taking that extra 15 miles.
Shared route
From Findlay, Ohio 45840 to Worthington, Ohio via US-68 S and OH-31 S.
1 hr 42 min (85 mi)
https://maps.app.goo.gl/nAm2eRRZx1euMwRb6