At first glance, ND does seem overrated at #20 but I think everyone is overreacting to last year. Let's look at ND the last 5 years and I think you'll see that with 15 returning starters (only 8 last year), they at the very least, deserve some love for being much improved in 2017.
In 2012, the Irish were a legit Top 5-10 team. Obviously, they were out-classed against Alabama in the title game but still had wins over Michigan, Michigan St, USC, a win over a Top 10 Oklahoma team on the road and a win over a Rose Bowl winning Stanford team.
In 2013, they won 9 games despite losing QB Golson to academics prior to the season. That probably cost the Irish at least 1 win and maybe even 2. They would've been a legit Top 15 team with Golson.
In 2014, ND was 6-0 ranked in the Top 5 and had defending National Champ Florida St dead in the water on the road. ND lost that one controversially in the final seconds and then were decimated by injuries on defense down the stretch. They were a bit healthier in the bowl and proceeded to beat a talented LSU team.
In 2015, despite suffering 8 season-ending injuries, ND lost to eventual National Champ runner-up Clemson by 2 on the road and then were a 45-yard made Stanford FG on the final play of the game in the final game of the regular season from being 11-1 and in the hunt for a CFB Playoff appearance.
With regards to last year, you'll get no beef from me in that it was arguably the worst job of coaching in the history of Notre Dame football. However, the Irish were very inexperienced (only 8 returning starters, 2nd least in entire country) and lost 7 games by 8 points or less. Advanced stats metrics like Bill Connelly's S&P still had the Irish power-rated as a Top 30 team despite the 4-8 record and even I still had them power-rated around 40-45 at the end of the season.
Clearly, we'd all agree at the end of the season, USC was a legit Top 5-10 team. However, if you watched the USC/ND game closely last year, ND was not out-classed talent wise with maybe the exception of USC's Adoree Jackson. ND was only out-gained 412-408 and USC benefitted from 3 non-offensive TD's.
Now when you flip forward to this year, ND is much more experienced and I believe they have elite talent at TE (Mack) and OL (Nelson and McGlinchey), all possible future NFL 1st-rounders. They also have very good talent at RB (Adams and Williams) and also at WR (St. Brown). The defense, again is a big question mark, but there's no question they made a major upgrade at DC with Elko.
With all this being said, I still think this is only a 7 or 8-win type of team because of their brutal schedule but on pure talent and experience alone, this is a team deserving of Top 20-25 consideration.