Yeah you're right. If I learned one thing from this match-up, it's that picking Ragna = Free win. If only her special moves were more useful instead of being combo filler most of the time.
So yeah, instant block everything and you might win. Bait dp as well and watch his meter. Run away after teched throws. Seems simple right.
Also, I learned that charging is like a taunt that works. The opponent usually thinks they can get a free hit in. Instant air-dash back or a good backdash can make a 5B from Ragna whiff. Then you can dash in and 5B to start the offensive or if you were in the air, you can 214x.