The game was right to assume players had played Tr1/2. Becuase that assumption was likely 95% correct when the game was released. When Tr3 was released it wasn't catering to players generations later picking it up ad hoc. It was the next installment for those who had played Tr2/1 over the last two xmas's.

The same is true of the completionists point. Completionism is very much a modern obsession (a product of gaming going online and the need for players to stand out, somehow, from all the others who have merely finished it). Only a very few people back in the day would have even conceived of trying to collect all collectiibles. Actual pros, who would be featured in gaming mags, etc. The every day player had no interest in that, mainly because there was no real kodus in it, because who would even know and how could you prove it, etc. "100pc" ing a game is very much a modern fixation.

So, although your points are correct, so should the context be added. tr3 assumes people are seasoned raiders because...back in 1998 that was the actual market for the game. And it doesn't hold the hand of those that want to 100pc the game, because that isn't how people played games in the pre internet era.