The Tamyia connectors are inherently inferior to the high current plugs like the Dean's and Traxxas plugs. So, yes, that adapter can limit current flow. Will you notice a difference in vehicle speed or run times? Probably won't be enough to notice, what you will probably notice is that the Tamyia connector gets warm to hot (depending on it's internal connection and current draw.).
The ideal solution would be to change all the batteries from the Tamyia connection to the Traxxas plug and skip using an adapter.