As a battle-scarred Sh***le veteran, may I offer these added points to your comprehensive review of this operation, imkeww

The ESOP limited Shuttle to 900 mile trips and not between defined UA hubs. (At the time, LAX was not a hub.)

Unlimited, complimentary upgrades to Shuttle's 8 F seats were offered to UA's highest level frequent flyers to avoid erosion of this segment. When Shuttle launched, seat assignments were available only per airport control. Shortly after, they became available for advance assignment to UA's frequent flyers at the top two levels.

DEN Shuttle ops were limited to LAS and PHX.

Initially Shuttle was positioned also to compete head-to-head with WN at OAK. Service was started OAK->LAX/BUR/SEA. However, within the first year, UA was unable to compete with WN's OAK fare structure which was consistently below UA costs and UA abandoned all OAK service except to LAX which was supported by the need to feed LAX's transcon/int'l ops.

Delays at SFO had a devastating effect on Shuttle operations. Whenever low clouds or fog prevented parallel approaches to SFO's two arrival runways, traffic from distant destinations was preferred and short-haul flights were often ground-stopped by the FAA at their airports of origin. This led to 2-4 hour delays and cancellations and many mis-positioned Shuttle aircraft. The ONT->SFO Shuttle route suffered notably because of this and ONT travel shifted appreciably to WN which did not suffer appreciable delays into SJC and OAK.
In the last two years of Shuttle, it operated on a "closed loop" with DEN/PHX/LAS/LAX/OAK flights to isolate them from transiting to/from SFO.

This was an attempt to keep flights to those five destinations on-time. This worked often but not always as poor weather and crowded airports in the late '90s occassionally plagued DEN/PHX/LAS.