Ti is never stupid but might get lost in the details,
Really, there is no substitute for Ti. It is without par for what it is.
of course Ti can be stupid, any function can. Stupid Ti would not understand logic in something that is obvious to smarter Ti(but the perceiving function needs to give same info for both Ti's or this not understanding might be cause by the perceiving function missing something), or would see logic in something where there actually is no logic because not trying to fully understand something before making the judgment if it is logical or not(some things might look logical on the surface, but after you look at it from different angles/more deeply you might start noticing something that brakes the logic in it).
"Where wisdom reigns, there is no conflict between thinking and feeling."
— C.G. Jung