Compared to those from the professional eras of full substitutions who are pictures of long term health?
No.
Simon, you've spent too long in America. You've become infected with their
"if its not a 100% fix then don't fix it" mentality (see the gun debate)
Take a look at the Laws at the beginning of the professional era, beginning in 1996...
[LAWS]LAW 3. NUMBER OF PLAYERS
(3) Replacement of players shall be allowed in recognized trial matches as determined by the Union having jurisdiction over the match.
(4) In
all other matches, a player may be replaced
only on account of injury and subject to the following conditions:
(a) Not more than four players in each team may be replaced.
(b) A player who has been permanently replaced must NOT resume playing
in the match.[/LAWS]
So NO substitutes, only injury replacements, and only four allowed, and the injury replacement had to have a doctor's approval. This remained in place until the term "Substitutes" was introduced in the 2000 rewrite...
[LAWS]LAW 3 – NUMBER OF PLAYERS
DEFINITIONS
A team consists of fifteen players who start the match plus any authorised replacements and/or substitutes.
Replacement. A player who replaces an injured team-mate.
Substitute. A player who replaces a team-mate for tactical reasons.
3.8 THE DECISION FOR PERMANENT REPLACEMENT
(a) When a national representative team is playing in a match, a player may be replaced only when, in the opinion of a doctor, t
he player is so injured that it would be unwise for that player to continue playing in that match.[/LAWS]
So we now had 7 players on the bench, and tactical subs were allowed, but an injured player could only still only be replaced if a doctor said so, and there was no requirement for any of the bench players to be a front row player. That didn't come in until a law change in 2003...
[LAWS]3.5 SUITABLY TRAINED AND EXPERIENCED PLAYERS IN THE
FRONT ROW
(d) When 19, 20, 21 or 22 players are nominated in a team there must be
sufficient front row players to play at hooker, tight-head prop and loosehead
prop who are suitably trained and experienced to ensure that on
both the first and second occasions that a replacement in any front row
position is required, the team can continue to play safely with contested
scrums.[/LAWS]
This remained in place until the Laws around front row payers on the bench changed again in 2014
[LAWS]3.4 PLAYERS NOMINATED AS SUBSTITUTES
(a) For international matches a Union may nominate up to eight replacements/substitutes.
(b) For other matches, the Union or match organiser with jurisdiction over the match decides how many replacements/substitutes may be nominated to a maximum of eight.
3.5 THE FRONT ROW - REPLACEMENTS AND SUBSTITUTIONS
(a) The table below indicates the numbers of suitably trained and experienced players available for the front row when nominating different numbers of players
Number of players and minimum number of suitably trained and experienced players
15 or less Three players who can play in the front row
16, 17 or 18 Four players who can play in the front row
19, 20, 21 or 22 Five players who can play in the front row
23 Six players who can play in the front row[/LAWS]
So now an extra player was allowed making 8, but that player had to be a front row player, so nothing was really gained in terms of tactical substitutions
Now that we have reached this point, there will be a problem if you reduce the number of substitutes from 8 to 4 as they suggest. Having
"8 on the bench but can use only 4 and then just to replace injured players." when three of those players will have to be front row players will only allow you ONE injury to the other 12 players on the field. If your 1st 5/8 gets injured, you can replace him. If your fullback then gets injured you're fecked because you can't replace him - that will take away a front row injury replacement, and could result in you later having a man-off situation with uncontested scrums if front rowers get injured.
At the professional level, this will almost certainly lead to players playing on with injuries, a situation that Rugby Union has bee doing its best to avoid.