Not tons of those (at Temple Meads a 06:34 arrival from Severn Beach, a 06:48 from Westbury which is scheduled to reach Cardiff 13 minutes before the Paddington – Swansea train, and a 06:53 from Gloucester, which calls at Bristol Parkway anyway. The only other service at Bristol Parkway in the 30 minutes before the Swansea train departs which doesn't start from Temple Meads is a 07:02 arrival from Gloucester (and the 06:59 from Swansea)).
It's the only train from Bristol Parkway to Cardiff between 06:30 and 08:00 and I suppose an extra direct Bath / Bristol - Cardiff (/ Swansea) service at that time of day makes sense, so presumably Temple Meads and Parkway are each well-used enough not to be skipped.