Don't know if it would improve player retention. It might take longer to grow really huge, but it might also get boring quicker.
I think the problem is that if you make it hard enough, have profit margins low enough, that growing huge takes much much longer, even with a good start and not much comp, then you've also made it so hard that minor mistakes become fatal, especially if there is comp. If you make it easy enough that minor mistakes can be overcome relatively easily, and it takes obvious, major mistakes to BK you, then people who make less mistakes and are very efficient will be growing huge at a relatively fast rate.
To me, and especially after trying to run this airline, the problem is more in the relative difference in profitability between 737/a320/MD90, LH, 50-60 seat turboprops, and <30 seaters. 2-3 years in, and the most viable airline in terms of plane availability in MT is to use turboprops. MD80s are just starting to become available now. But turboprops, even if you use them reasonably well, are likely to bite you with overhead & maintenance, it's much harder to build an all-turboprop airline than an all-150 seater airline, given similar plane availability.