its not a deadlock, itachi is clearly above them both and his weakness is not taijutsu, if he and gai fight in taijutsu base itachi will certainly win even kakashi has kept up with gai base in taijutsu, now if u are saying gated gai taijutsu is itachi's weakness then of course gated gai's taijutsu is everybody's weakness even Godara's as u can see...just because one person is visibly better than u in taijutsu(gates) doesnt mean its your weakness, all u are doing is trying to put itachi with kakashi and gai but he clearly is better than both and wouldnt even allow gai to enter the 8th gate let alone allow kakashi to use kamui, that whole feet watching method gai says he uses on the sharingan has never gotten gai the win over kakashi so why would it work on itachi...
.not only that but itachi is better than kakashi who is on par with base gai in taijutsu and the sharingan has read movements as fast as A's and killer bee's and both of them are way faster than base gai also obito easliy read base gai's movements even while his nun chucks and even caught them barehanded...itachi ha sonly one weakness and thats his terminal illness