Definitely not. It goes over Dartmoor, which for obvious reasons would be slower than the flat route via dawlish
During the 1950's the journey times from Exeter St David's to Plymouth North Road where almost the same for both the Southern Route via Okehampton (skirting the North Side of Dartmoor) and the Western Route via Newton Abbot (that Skirts the south side of Dartmoor).
Whilst it took a few minutes longer to go via Okehampton it must be remembered that the southern line was a few miles longer, so average speeds were very similar.
If rebuilt the Old Southern Route could be brought up to a higher standard than before with increased line speeds and curves relaxed.
But the DafT spend that sort of money on Railways, DREAM ON!!