That's true, but the English settlers also could call in backup as well as most critically, supplies, from the mother country. Not many supplies will be forthcoming from Iceland and Greenland, least of all Scandinavia.
I don't think the Greenland settlement called in any supplies from Iceland. They seem to have done OK without them.
We can estimate there were between 2,000 to 3,000 Indians on Newfoundland based on how many there were when the English showed up centuries later. Greenland had no more than 10,000 Norse scattered in three settlements, and Iceland around 50,000, maybe a bit more. Norway had about 450,000. How many people of these people will abandon Greenland and Iceland in a longship to go to the edge of the world, far beyond contact from civilisation? The shipping is very very difficult in this era, after all.
The Beothuk numbers are really old. 19th century. More recent estimates puts their numbers at 400 - 700 individuals at the time they encountered the English ( Marshall, A History and Ethnography of the Beothuk) Numbers at the time of the Norse are likely to have been marginally lower.
However, that is not that important. What is important is that the Beothuk lived in family bands of 30 - 50 people (less than the crew of a single longboat), across a land bigger than Ireland.
While Greenland maxed its population at 5000 people. These lived in farms around churches, with groups of these being a settlement. The biggest of Greenlands three settlements probably maxed out at about 2500 - 3000 people. In the more clement climate of Ireland, a Norse town with little in the way of hinterlands were estimated to be 4000 + people.
This is the Beothuks essential problem. If Norse settlement gets going they are not going to encounter the Norse as a unified force. They have no societal mechanisms for anything like that. A Beothuk family band of maybe 40 people will encounter a Norse settlement area of maybe one hundred times their numbers. And a hundred to one is their
best case numbers.
Even initially, the Norse settler pool from Greenland and maybe Iceland, outnumbers them. Eric the red probably left Iceland for Greenland with 2x their maximum population.
(And even if they did manage to join every Beothuk from an area bigger than Ireland together in one force, they would still be outnumbered maybe ten to one by one Norse settlement. What saved them was that the Norse did not know this.)
And
then the Norse population will start growing....
Essentially, the Norse uses the available food resources far more efficiently. That means that at the point of contact, the Norse will massively outnumber the natives.
And... I don't think there were any agriculturalists in the Eastern North America around the time of Eric the Red. I think that came during the next 500 years. I could be wrong though.
All that is before looking at the situation with diseases...