I've also found it rubbish hence I'm now using Google Maps via CarPlay.
No system is perfect but it helps if you understand its limitations.
RTTI is good at traffic flow information and will add all the delay minutes to a journey with no consideration about future trends or what might happen.
So for example, if you set off at rush hour on a 5 hour journey it will add say 45 minutes traffic because 2 hours down the road you’ll go through a city that’s currently congested but won’t be by the time you get there. Google, for example, will factor this in and likely show no traffic delay because it knows that by the time you get there, it’ll most likely be fine. However, imagine there is a serious accident on the Motorway 2 hours ahead. RTTI will add the delay onto your journey immediately so you’ll know something big has happened. Google however will calculate that it’ll probably get much better – even though it likely won’t – and therefore won’t necessarily warn you of it.
So in summary, RTTI shows total delays on your route. Google shows expected delays on your route based on previous trends alongside current information.
I have lost count of the number of times Google traffic has told me everything is fine when the reality is that there is a serious incident that has closed the motorway. Google is also notoriously bad at closed roads too and often interprets a road with no traffic flow as a completely clear road unless somehow somebody has manually intervened.
For this reason, I find Google maps much more helpful in managing journeys with conventional congestion – ie at rush hour. I find RTTI/TMC combined much more helpful at managing journeys with non-conventional congestion – ie accidents etc.
Given that most of my nav usage is for long journeys I find RTTI very useful and would not want to be without it. If most of my usage was a regular commute then it would be less helpful and I’d probably want to be using Google maps, instead.