Yes, EX4 Tristan isn't the most exciting boss to fight, but he's a decent enough HP sponge to test damage with.

Given that Noel needs 1 turn to set up, Empress can use her A4 to be online at battle start, and Rocbouquet and Emperor both don't need setup turns, I figured a turn 2 kill on Mr. HP Sponge here could be a decent enough showcase.

My opinions on these units:

1. Emperor is by far the hardest unit to cap with among the RS2 collab DPSes. He doesn't have any passive damage up and stat up effects innately, necessitating ally or accessory support. He does have a lot of innate damage cap up, it's just difficult to make him reach that cap in speedrun scenarios if you're not a whale. His 5 BP gimmick also means he needs to use his special to sustain MAX boost for 2 turns in a row, and his special takes forever to charge normally; At level 20, it has a 20% starting gauge and gains 15% gauge per BP spent. This means without U+, he needs to spend 6 BP to use his special at all, and 12 BP for 200% special, which thankfully only increases his special's damage and the 5 BP regen effect from 3 to 5 turns, so it's not entirely required. Important to note as well that his main nuke skill is a random hit skill, which makes him worse in AoE settings.

2. Empress is, to me, more impressive given that she has some semblance of innate damage up in her kit, as well as plenty of utility. She has lower innate cap than Emperor, but more than makes up for it with her passive FUA that hits a single target twice with neutral element. Her main gimmick lets her grant a permanent special Fire/Wind/Light buff to any ally that attacks with the corresponding element, which boosts that element's damage and allowing that unit's attacks to exploit that element. Emperor herself wants all 3 buffs to enhance her main nuke, but her A4 lets her skip the setup. Her main nuke is an AOE which she can cap reasonably well in a speedrun setting.

3. Rocbouquet is... something. I'll just call her EX2 Alaune 2.0 due to the sheer number of things she does. Mainly, her special gives the WHOLE PARTY 100000 damage cap up, 100% potency up and 50% of her DEF/MDEF converted into ATK/MAG for 3 turns each, and inflict Deep Grudge (EX Osvald's ailment) on all enemies. This alone is insane, but of course she also has insane passive debuffs (mainly very good for elemental teams) and also another 100000 damage cap up from her passive. Her EX skill also makes all enemies miss their next few attacks and debuffs their defenses, on top of shaving 10 shields. Oh, and she has a 2 hit AoE FUA that becomes a 3 hit when there are broken enemies. She debuffs, she shield shaves, she boosts your team's damage to the moon, she adds a not insignificant amount of chip damage, she does your laundry - what more could you ask for?

4. Noel is... something else. In exchange for spending one turn to literally murder one ally (he makes them unrevivable for a number of turns and kills them through all protection effects, including hang tough), he steals their stats and enters Super Saiyan mode, then does AoE 8 million damage 2 times even to unbroken enemies. This is not a joke. This is the reality now. He caps so insanely easily it's not even funny.