If you specifically meant mobile, you could have said so. Your statement was, "every other client has even more drawbacks when it comes to E2EE." Nheko disproves that statement. It also suggests that some alternative mobile clients might handle E2EE at least as well as it does. You might want to try them.
By the way, text search with end-to-end encryption happens to be tricky to implement, and Matrix projects aren't funded by corporations with deep pockets. Tempering your expectations regarding development speed is probably worthwhile here.