I am not sure why you are saying it when we have numbers that prove it wrong. In the playoffs, the starting lineup played 112 minutes together, during these 112 minutes the stats look as follows:
Def-RTG: 103.1 (That's elite defense, better than their 370 minutes together in the regular season).
Off-RTG: 124.8 (That's elite offense, almost by 6 points over their regular season)
Net-RTG: 21.7 (That's bonkers, they were clobbering Denver with that line-up).
The Blazers defense failed in just about any other combination. If you look at this series, there were only 2 5-unit lineups that had more than 20 minutes through the entire series - and both of them had fantastic results (The other one is replacing Nurkic with Melo which was actually even smaller). All other combinations played very little together because they were so bad.
But, size was not the issue for the Blazers defensively. It was the large amount of bad defenders on the roster. Last year, the Blazers had 4+ defenders on the roster (Nurk, Roco, Powell, DJJ). DJJ's offense was so bad that his defensive plus was neutralized.
Norm or Norm's size was not a problem for the Blazers when he had other good defenders next to him - he is a better defender than you give him credit for and while I am sure there are times his size is a problem - it is nowhere near the problem you believe it is. Even that Dame, CJ, Powell, Melo Roco lineup was not horrible defensively (it was not great, but it was not horrible) against Denver. That lineup was actually mind boggling good on offense so it's 109.8 rating on defense was fine.
If you look through the entire playoffs across the league. If you do a 5 units with a positive net-rating that played at least 100 minutes, this lineup was 3rd best defensively in the league.
https://www.nba.com/stats/lineups/a...DEF_RATING&dir=-1&CF=NET_RATING*G*0:MIN*G*100