When rating a GT route we probably have to keep in mind that AOS/RCS may not be able to swap stages the way they (we) want to make the overall route better. As of some locations may pay to host a stage on a certain day hence you can't do the stages in reverse order. Of course that's just assumption, so if someone has more knowledge, correct me.
However, this is not a huge issue with this route. Mountain stages could've been better by simply adding a pass or so. Now we get goo mountain stages finishing on a really hard climb...actually discouraging riders to attack from a far.
Add to that the small number of TT km's ant disappointment is huge.
That said, I don't think a long(er) TT would make the race better as we have good TT riders that are genuine contenders. Bar for Rog, Pog, Vingegaard if he confirms 2021. And all of them would target the Tour 100% The only way to draw Pog in for me is to have 2012 Tour like Giro route. That leaves us with only Almeida as a very good TT'er among the GT contenders.. Yeah, one could say Thmoas, Tom D and Remco, but Thomas will do the Tour (likely), Tom D is probably done GT wise and if Remco proves to be good enough climbing wise in a GT, he'd be good enough on this route, Not to mention, he won't/wouldn't start anyway.
However, while more TT probably won't really impact this Giro, it certainly impacts GT's long tern. As this way you attract Bardet-like climbers and that doesn't make it for a better racing.