Not really - it just sounds a bit limp! The emphatic construction, as in the example, is used much more often in Welsh than in English.

(And it would be 'mae xxx yn wlad braf' - soft mutation of gwlad.)

No, ydy/yw is used in other patterns as well.

Here, the sentence is an emphatic one, so the thing being emphasised - gwlad braf - is moved to the front of the sentence, just as we do with people's names or jobs and so on. If the sentence is started with a noun (including a name or a job title) or an adjective, then the verb-form is ydy/yw rather than mae:

• Sioned yw hi - She is Sioned.
• Meddyg yw hi - She is a doctor.
• Meddyg da yw Sioned - Sioned is a good doctor.
• Menyw dal ydy Sioned, nid byr - Sioned is a tall woman, not short. (Emphasising the fact)

But:

• Mae'r tywydd yn braf - The weather is fine. (No emphasis)
• Mae Cymru'n wlad braf - Wales is a fine country. (But not emphasising it)
• Mae Sioned yn dal - Sioned's tall. (But not emphatically so)

Emphasis is used much more often in Welsh than in English.