Nexus Clash

Assuming 100% accuracy, and full Combination trees, thee effect of Critical Strike is one of the following:
(The base effect of Combination is a bonus of 0/3/6/9 damage, the bonus averaging at 4.5)

1. Skipping the first strike, yielding a 0/6/9 nice combination with average bonus of 5 damage
2. Skipping the second strike, yielding a 0/3/9 nice combination with average bonus of 4 damage (yes, average bonus goes down here)
3. Repeating the last strike, yielding a 0/3/6/9/9 nice combination with average bonus of 5.4 damage

There's also the possibility of multiple Critical Strikes on a single combination, which make it slightly better, but not much, and muddle the case analysis.
Baseline, Critical Strike improves Combination Attack by roughly a 20% when triggering, or 0.9 bonus damage, due to cases 1 and 2 cancelling each other out. This, combined with the 33% chance to trigger, improves Combination Attack a 6.6%, or by an average bonus of 0.3 damage.

Not assuming 100% accuracy, the effect of Critical Strike improves, as it's uncertain whether you'll be able to access the later effects of the Combination. This makes Critical Strike significantly more attractive at earlier levels, when the Myrmidon's accuracy is low, but a waste of 20 CP later on.
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Replacement suggestions:
Replay
The Myrmidon gets 2 attacks at the final step of the combination, instead of 1.
Dragon's Rage: Instead of removing the reset, possibly increase max combination +1. Alternatively, increase the damage of every combination tier. Alternatively, always start combination at tier 1.

Instinct
X% chance of triggering the maximum combination effect, resetting the combination.

B4 Critical Strike
It was an interesting mechanic, though maybe with reduced bonus and increased chance.

Devs have a plan developed already for rebalancing this.