Don't agree. For every bus in the city, there would need to be two trams - or one double-length tram. With the amount of buses there are in the city centre (and the real problem is cars in bus-only routes), nothing would change.
At least buses can overtake at many points, rather than waiting for an overtaking line.
Cities that have re-introduced trams are finding that far more people use them than ever used the buses. Everywhere they've been introduced, it has resulted in improvement.
Also, for some reason, the more selfish motorists are likely to get in the way of buses, or try and get past them if they think they can; they don't get in the way of a tram!