In some larger strings, the consistent types are kept in a string even if they are not competitive, because the trainer gets a better rate with a larger block of stalls.
I wouldn’t call what you described suspicious - it could be he was kept for any number of reasons: stall rate discount, he could have been the sentimental campaigner of his connections, he could have shown promise in workouts but fizzled in company, etc. If he cost the connections a lot of money and they were not necessarily a huge outfit, they could have held onto him a bit longer because they were hoping that talent was there.
With 30 starts expect natural wear and tear associated with the track. Like WheresMyWhite said, you’ll likely find some wear (remodeling) that requires maintenance versus immediate attention. Horses who are fundamentally unsound would never make it to that number of starts so your baseline soundness is good. What his future soundness looks like depends on if he obtained any injuries during racing that handicap his body going forward.
The national average (US) of starts is something like 6 starts, but 15-30 starts is not uncommon and you will find tons of these horses at the cusp of their career’s culmination in “lower” end tracks.
A slightly divergent topic, because this comes up often on COTH and other boards about Thoroughbreds: Don’t let the designation tied to their name fool you - that is where they were born, not how they were bred. Many horses we see with (IRE) or (GB) or even (AUS) are almost entirely NA bred on paper. Resellers will say things like “Irish TB” or “European TB” because their horse has (IRE) or (GB) as their designation and they think this correlates to its inherent quality – but then you look at their pedigree and they’re by Street Cry out of a Storm Cat mare. Lol.
There is not a significant difference in the quality of TB in US versus overseas. The more important difference is the type of tracks. US is almost entirely dirt tracks. GB and IRE are turf. GB’s leading sires like Sadlers Wells and Galileo are North American (US / CAN) on paper despite where they were born; they are all part of the same gene pool with the exception of several GER horses, whose lines have gone totally extinct in dirt racing with the exception of a resurgence of horses like Surumu and Lombard (Allegretta, Galileo’s dam) who have started to trickle back into US bred horses through stallions like Animal Kingdom and Galileo. Australia has a whole dynasty spinoff of horses from Danehill (Northern Dancer), but even their leading sires are almost entirely commercially NA on paper – like Danehill, Snitzel, and Street Cry. The best TB stallions in the world come out of US dirt breeding - AP Indy, Storm Cat, Sadlers Wells to name a few.