Having a full tech tree just means you have a lot of endgame options but having no civ bonuses means you have nothing in the early and midgame that stands out. This type of civ would get absolutely rolled in RM 1v1’s because any other civ would be able to exploit their civ bonuses at some point in order to gain an advantage. They’d less of a disaster in RM TG’s but decent at best.
The closest civ we have to this already in-game would be the Chinese but even they get a farm team bonus and a discount for researching technologies. You gotta have some bonuses, even if it’s something silly like technologies (except going to the next age) research twice as fast.
They’d be very good in DM where eco bonuses don’t matter. Any civ with siege onagers, siege rams, and halberds/paladins have a nasty end game.