No need to join an alliance. Just add another campaign.
I was competing against a huge airline in MT3 who's HQ was Tokyo Haneda and bases in Narita and Fukuoka. I was based in Fukuoka, flying all B737NG-fleet, some 30 aircraft. My competitor had DHCs and 737NGs, if I remember correctly. My CI was initially 20-30, my competitor at 100. I was making a profit of $1-4 million/week. At the end of the game, I pushed up my marketing and reached CI of 70. This cost me $20 mil/week. In the end, I only received a 15% boost to ticket income (from ~$28 mil to ~$34 mil). This result might not be generalized, but still shows that you can do well with low CI if other aspects are ok. Though I have to admit, that my competitor didn't really try to push me out, as he only served max demand, and sometimes not even that. I also had some routes where he wasn't flying.
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