the 204 has the same turn time as a 757
the 204s pax capacity is slightly smaller than the 757
the speed is within .01 mach
The only major difference is the really weak range of the 204...
the 204 uses a ton more fuel than the 737
That "only difference" is a mighty big one, since range is ultimately the defining characteristic between most aircraft. Compared to the TU-204...
A 752 seats about 10% more passengers.
A 752 consumes about 20% less fuel
A 752 can carry those passengers almost twice
A 10% increase in revenue with a 20% decrease in fuel costs is HUGE. That's north of a 20% per-seat pricing advantage over the competition -- i.e. where a 757-200 could turn a profit at $100/seat, a TU-204 would need to charge $120.
Now compare the TU-204 with a 737-400:
A 734 seats about 10% fewer pax, so you lose revenue, BUT
A 734 uses a full 35% less fuel
A 734 still manages to have significantly more range than the Tu204, in the range of 200-1000NM more
A 734 takes only HALF the turnaround time (which can easily make up for the 10% fewer pax in many cases)
A 734 requires 1200ft less runway to land, the Tu204 runway req limits its capacity at many locations, reducing its pax advantage greatly
A 734 requires 20% less flight attendant staff
A 734 is much closer in upfront costs and, after consider major maintenances, will likely cost less in fixed costs than a TU204 and save many tens of millions more in variable costs
In the end, a TU-204 is FAR more closer to the 737 than a 757. It's a a 734 that seats 18 more people, sucks about 35% more fuel, doesn't fly as far, and needs more runway and staff to operate.