This has been covered at length on previous threads.
Prior to April 2016, Toyota operated a fixed price service scheme that offered the Intermediate, Full and Full+ services together with service options. Service options were things such as brake fluid change, which are supposed to be carried out every two years. So owners often had the situation where they were booking, for example a full service, and finding there were additional items to be done at additional cost that were required by the service schedules. See https://www.toyota.co.uk/owners/service-mot-maintenance/servicing.json
In April 2016 Toyota revised both the service costs and the services - and the majority of the service options were included within the revised service schedules.
Toyota also included a cheaper service regime for vehicles over 5 years of age called Essential Care.
As regards the Hybrid Health Check (which is where the hybrid system and battery are checked for correct operation, etc), this is done free of charge at each service by a Toyota dealer. If owners have their car serviced elsewhere, they can pay a Toyota dealer to carry out the Hybrid Health Check. The extended battery warranty only comes into effect when the hybrid components/battery warranty expires (5 years/100,000 miles on new vehicles first registered from April 2014). See https://www.toyota.co.uk/owners/warranty/toyota-warranty.json
Once one's vehicle reaches five years of age, one can take advantage of the Essential Care scheme provides a silver service (intermediate) for around £100 currently, and a gold service (full) for currently around £180. This is similar to schemes other manufacturers offer for vehicles outside the new car warranty - and cheaper than some.
Toyota's service intervals are either 1 year or 10,000 miles, whichever occurs first - so by the sound of it your car has been correctly serviced on the time basis.
Yes, as with any manufacturer, one can have one's car serviced by a VAT registered garage, rather than within the franchised dealer network. However, should a warranty issue occur for which correct servicing may have had a bearing on the issue, it would be down to the owner to prove that the correct service schedule and parts of sufficient quality had been used. Servicing outside the dealer network would usually deny the owner any goodwill help from the manufacturer in the case of major repairs, etc outside of the new car warranty - this is the case with any manufacturer, not just Toyota.
Also outside the franchised dealer network, any required customer service campaigns or recalls won't be actioned - these would need to be done within that manufacturer's dealer network.
At the end of the day, one would expect service costs to be looked at by the prospective purchaser before the purchase of any vehicle, and certainly with the 21 new vehicles I have bought from the likes of Nissan, Honda, Mazda, Hyundai and Toyota, I've checked the servicing costs before purchase. From my experience of other Japanese/Korean marques and ignoring service packs which Toyota don't offer (not service plans), Toyota's service costs are competitive despite last years cost increases and schedule changes.
As always the choice is with the individual.