Picked up FF13 again yesterday. I was around 80+ hours in, so probably the same level as you guys.
I only had one mark left in the Titan Trials last time (well, 1 mark and a ??????).
The guy was way too hard for me then. Yes. I'm talking about you! E1's Neochu!
It seemed ok in the beginning. Started with a Libra and a COM/SYN/SAB for the first round. Then bashed it with RAV/COM/RAV. Till its first Screech cleared my party like dust! I tried summoning to skip the Screech, but even with that I could only take it down to ~70% HP before it's kids (pikochus or whatever. raptors...) massacred my team.
Got fed up. Left and leveled-up at the straight path with the Sacrifices. Sold lots of Perfume and got Lightning's final weapon upgrade (FF13 citizens sure like perfume!). Went back to Neochu.

I could survive the first Screech now, without wasting a summon. Even survived the kids. Until a 2nd Screech... and I'm downnnn.

Grinded more. Got Fang's final weapon upgrade. My party had maxed their 2nd role to Lvl5 by now and nearly maxed their 3rd.
Went to settings to set the battle-speed to slow.

Tried again. Survived the 1st Screech. Kids popped up. Summoned when the 2nd Screech came. That got it down to ~20% HP remaining.
Still had 5 kids running around madly. Used Quake. Switched to RAV/COM/MED for a last rush at Neochu with 2 of my members continuously in the red for 4-5 turns, one of them my Leader.

But it worked!

Switched straight to MED/COM/MED to take the 5 kids on in snail-speed. saaaafe~

Now I just need to find out what that line of ??????? is. So I can give up fighting it.
I also had a try at one of those big turtles. Got it down, then got it to ~15-20% HP left. Might actually be able to take one of them down with some luck.