You are exactly right that once again the bottleneck will become discovery. Given that developing a bot is easier and cheaper than developing apps, I wouldn’t be surprised to see a proliferation of bots that is 10x larger than apps.
It looks to me that the meta-bot, i.e. the gatekeeper that is likely to capture most value, is the chat app itself (facebook messenger, telegram, LINE, kik). Unless people will keep using several chat apps and maybe another unifying intermediate layer is needed/wanted.