Early couple of years Theoben was getting its system together. The gasram worked but they were buying Webley barrels. Think their triggers were Webley inspired too. All in they were expensive.
Once they got the barrel sorted from Germany and the rest put together then they were glorious if a bit high ticket priced. The only "average" thing was their triggers which were equal to any FWB but not a Rekord. No one had done a better trigger than a Rekord.
Early FT years it was the HW77 that was heavy, accurate, and had the right trigger. FWB Sports were outclassed as was everything else. A well sorted tuned HW77 can still deliver competition winning performance in the right hands. But wow what a lump.

The other truth is that Theoben gasrams are half as hold sensitive as a standard springer; which isn't PCP easy.

Distractors are either not happy with the trigger, don't care for the high ticket price (fab woodwork, engineering, and bluing), or that they don't shoot like a PCP. Those who were brought up on springers think they are fantastic and only equalled by an Air Arms springer. And thats because Air Arms can do a better HW77. And still a HW77 fettled well is a great rifle too.

Springer or gasram takes a certain technique. Both old technology compared to a PCP.

I shoot regularly a Fenman .177 that has accounted for many Magpies and rabbits. I have a SLR88 which tack drives too. All the Theobens I've had, a good ten, have shot very well indeed.
Of the non Theobens then the HW90 is a brilliant rifle.
I'm not too concerned about spare parts as I've never had one fail yet and my Fenman is 20 years old (sent it off for a service and the reply was nothing was required). I'm sure there will be someone somewhere with the servicing skill to keep them running for years and years.

Lastly, buy good examples while you can. Because they are not a PCP they are interesting and testing to shoot, which to some is the fun of older rifles. I can head shoot effectively all the farmyard critters with one, what more is there to want?