Was it worth using a masterball on latias in heartgold
I would say yes just because latias roams and this makes latias very difficult to catch. Without using the master ball, you would have to use a move like block or spider web or have a Pokemon with shadow tag or you would have to slowly reduce its hp and keep searching for it until you weakened it enough to catch. But I would say, yes it was worth it.
Maybe. I'd say yes, but HG has a few random encounter legendaries and hard to catch regular ones, so it's really all down to your judgenent. Latias is really decent, though, so I think you made a good call.
No, I cannot say it was. You should have saved it for ho-oh as it has superior stats. (680, ho-oh, 600, latias)