The trains via KO were very handy for cross-London trips from Reading on a Travelcard, but you were lucky if you could catch one in both directions on the same day.
Around 1990 I used to be a regular on the Saturday am Reading-East Croydon (Manchester-Brighton) or the Reading-Bromley South (Liverpool-Folkestone via Chatham and Dover).
The Kent train soon became M-F only, and then summer only, while the Brighton was 6 days a week.
It was much the easiest way to reach the Southern system from the west.
At first trains ran up the GW main line to Old Oak Common East Jn to reach the WLL at North Pole Jn, but were rerouted via Acton Wells and West London Jn after the North Pole site was taken over by Eurostar and the direct GWML link dismantled.
At that time there were next to no local services on the WLL, quite different to today.
The WLL was electrified over the period I used the through trains (for Eurostar and class 92 - local trains and new stations were an afterthought).
I used KO itself a few times, but the LUL connections to Earl's Court were sporadic in those days (exhibition days only I think).
The Brighton trains also stopped at Clapham Jn for a while, but this stop was dropped first and then I think Kensington was also dropped before the trains finished going via the WLL.
The very useful Kent train was eventually cut back to Reading and then axed completely.
As for "comfort", they were decent standard BR XC Mk2 stock with a buffet I think, lightly loaded and a pleasure to use. The regular train crews were always very friendly.
The alternative via London terminals might include HSTs to Paddington, but otherwise was a old mish-mash of ancient DMU/EMU until the Networkers turned up (Turbos on the WR).
Plus the noisy and crowded Bakerloo across London.
But in the end, the main line frequency won over a tiny number of rather unreliable through services.
I remember vividly being told at Folkestone Central (waiting for the return Liverpool to appear) that it was "not one of ours" and was "operated by a different company" - in about 1991.