Why not upgrade to th10 premature?
I just recently started with th9. All of my defenses are maxed to th8 standerds other than 1 cannon and 1 tesla which are upgrading to th9 standerd. My walls are mostly skulls with 8 legos. All of my regular troops are maxed for th9 other than healer (lvl3). My spells are maxed th8 and my dark troops are maxed th8 other than hogs (lvl5) and minions (lvl5) and valk (lvl1).
I'm not sure I see a disadvantage to upgrading to th10 early.
Whenever I attack a th10 as a th9 I get destroyed due to the OP inferno towers. The base could have lvl 4 wizard towers and cannons, yet two IF's in the middle will wreck any army I throw at it.
So if I were to upgrade early and get my inferno towers I'd be relatively safe from th9's.
It would offer more loot for the th10's to attack me, but th10's attack me already so I don't see that as being a disadvantage.
Loot penalty. All the th10's I see are loaded, so I'd like to be attacking them more. Th9's I'd see a slight penalty, but still attackable. Add 20 more troops, maxed wiz and dragons and 1 more spell, I think it would probably be a bit easier.