ANGEL ISLAND 1
any%: able to use Tails to move during initial cutscene
otherwise runs are 100% similar

ANGEL ISLAND 2
runs 100% similar

HYDROCITY 1
any%: able to use Tails to fully zip the level
solo actually has to play the level. really slick looking!

HYDROCITY 2
runs 100% similar

MARBLE GARDEN 1
solo: uses a different, faster zip, but this is likely an improvement in the any% run as well
can't compare accurately

MARBLE GARDEN 2
is skipped in both runs

CARNIVAL NIGHT 1
both runs use the exact same zips, but slightly different methods of activating them

CARNIVAL NIGHT 2
completely different. i don't have the knowledge to figure out whether or not the different paths are specific to those character or if the solo sonic route is just improvements that would end up being implemented in any% anyway, but so far this is the biggest breaking point between the two runs

ICE CAP 1
solo sonic skips the boss but once again i feel like that's an improvement any% can use as well. rest of the stage is zipped over, same thing as carnival night 1: same zip, slightly different setup

ICE CAP 2
is skipped in both runs

LAUNCH BASE 1
full level zip, exact same in both runs

LAUNCH BASE 2
full level zip is the same in both runs
any% is able to skip one of the bosses and a fairly long cutscene

MUSHROOM HILL 1
full level zip is the same in both runs
any% is able to use Tails to break the victory cutscene

MUSHROOM HILL 2
solo sonic uses a different zip, once again i can't tell if this is specific to the run or an improvement that can be used in any%
rewatched: solo sonic is faster overall in the level, meaning improved any% would likely follow this while also being able to skip MH1 victory cutscene

FLYING BATTERY 1
full level zip, both runs are identical

FLYING BATTERY 2
full level zip once again, both runs skip straight to the autoscroller. solo sonic is faster, once again likely an improvement for any% as well

SANDOPOLIS 1
full level zip
solo sonic is faster, this definitely looks like it can be used in any% too though

SANDOPOLIS 2
ONCE AGAIN, solo sonic is faster through routing improvements that look like they all apply to any%

LAVA REEF 1
identical zipping, slightly different setups. solo sonic has improvements for any%

LAVA REEF 2
identical zipping

HIDDEN PALACE
any% is able to use Tails to quick-kill Knuckles
any% is able to use Tails to skip the rest of the level after Knux

SKY SANCTUARY
completely identical in both runs

DEATH EGG 1
once again, the routing looks different. weird bouncing around "hit the targets" thing is obviously much faster in any% but it looks like solo sonic route is overall faster (rewatched this: any% is 1 IGT second ahead of solo at the end, solo spends 3 more IGT seconds in bounce chamber while also entering it earlier due to the new route. target hitting thing likely the only difference between this and an optimized any%)

DEATH EGG 2
same zip, different setup, final boss is pretty much identical

OVERALL
biggest specific changes are in Hydrocity 1 and Hidden Palace
most differences are due to new tech that is likely implementable in any%, meaning the two runs would be almost entirely identical when any% is optimized
Hydrocity is the only skip that affects actual gameplay, all other Tails-specific zips skip bosses/cutscenes
for the most part every stage is the same except solo Sonic has different methods of activating the same zips

i don't think they're different enough