Travellers is a good series in and around itself but wouldn't compete with other time travelling genres like Dark, and other Scifi series in terms of pacing and script. It has its moments of Soap operaish drama which makes it humanly but also slow and boring at times.
In terms of science and time travel, it fails to explain what is the point of this whole exercise of travelling back in time to change the future and the grand plan. As by the end of season 3, we notice that it is not a single timeline as we see in series like Dark where the timeline is singular and when we travel in the past, we dont change anything as the past has already happened. It is most of the time our own acts of time travel that has caused certain acts in the past. In travellers this part is left very ambigous. For example the protocol Omega means that the Director has abandoned control of this timeline and the travellers are on their own. Now, it is possible to understand this as evident in that one episode where the director takes 9 iterations to save the Mcclaren and crew from being killed by 001 team. You can see that the director in reality abandoned the first 8 timelines and got it right in the 9th one. So, the people in first 8th timeline will anyway suffer a terrible faith as is preordained in the future.
So, this travellers team (Mclaren and team) are not changing the future for them as they are going to suffer anyway. They die in all those other timelines a terrible death except the one in which the Grand plan finally succeeds. So, This entire Grand Plan is beneficial only for the Director who is the only one who exists in all the timelines and is capable of seeing it through. For all humans, all the alternate timelines, they all die a terrible real death except in the one timeline in which the Director would finally succeed in saving humanity. When you understand this logic, you will understand that you can never change the past.