I have quite similar set-up, smart bike trainer for indoor workouts in the winter and gravel / mtb only with HRM and cadence sensor for the rest of the year. My approach is to have structured workouts in the winter time and ride for fun in the spring and summer. Xert works very well for me in that respect, as it fully covers my winter training needs and tracks training load and some other metrics for rides without powermeter.
Anyway, the answer to your question depends on your goals and expectations. If your are interested in structured workouts for your indoor riding, then Xert is always a very good and cost efficient option. But if structured training it is not your key focus and your are more keen on virtual racing, ride simulation etc., then other platforms have also plenty to offer.