Also, for most times from '05 to '11 he wasn't far behind rafa, except for 2008 french final.
2005-2011 is a LONG time ago. You do realize there is a huge different between late 20s and late 30s, no? Especialy on clay, which is not the surface of the old, as we see by even the clay GOAT getting his ass handed to him repeatedly at age 32 all season. Yes Federer was once a fanatistic clay player, today he is still a pretty good one, maybe a very good one on the right days with off days more prevalant than ever. His prime on the surface is eons ago. Nadal's prime on clay is also long past, but unlike Fed he was so dominant to begin with, and even he probably will have a hard time winning RG this year, particularly if Djokovic is there at the end.
I dont think he is being underrated. Many bookies have him 4th favorite behind Nadal, Djokovic, Thiem. Where do you think they should have him exactly, this is the highest he possibly should be. He is higher than Zverev who has won clay Masters in the last couple years, and was a quarter finalist at RG last year. Higher than 2015 champion and 2017 finalists Wawrinka, who has won 2 of his last 3 clay matches with Federer. So it seems he is rated just fine, some have him 5th behind Tsitipas which is the lowest anyone has him. And given his last couple tournaments and Fed's injury it makes sense Tsitipas is creeping past him in some of the bookies, but still nobody has him anything but 4th or 5th.
As for dismissing him winning the title well it would be a huge long shot/surprise. He has zero shot if he plays Djokovic, probably none vs Nadal given their RG history despite his success playing him lately, and only an outside shot to beat Thiem who will be that much harder to outlast/grind down in a best of 5. A match vs Zverev or Tsitipas at RG is probably a 50/50 for Fed at best, even Del Potro who gets up for those sort of matches, or Wawrinka who has done well against Federer on clay since 2014 or so even if he isnt the same player anymore. Beyond those 3 obvious ones who should beat Fed if they meet, and atleast 4 others who have atleast a 50/50 shot to beat him if they somehow cross paths in the draw, there are numerous other dangers to him from the draw behind all those guys. Just look at his 2012-2015 showings. Ok 2012 he lost in the semis to Djokovic as expected, but had some narrow escapes to get there. 2013 and 2014 falling to Gulbis and Tsonga keeping in mind Tsonga's worst surface is clay. In 2015 slapped silly by his pigeon Wawrinka. Anyone in the top 30 who likes clay probably thinks they have a fighting shot, and there are atleast 2 or 3 players he would have to avoid. Someone above listed the 13-16 seeds, all who will be a tough opponent for Federer in round of 16 should both get there, all capable of taking Fed out of RG at this point. Again 2005-2011 is a long time ago, his quality showings on clay in the last 6 years are few and far between, partly since he doesnt even play on it regularly anymore.
He should make the 2nd week but he also could be vurnerable to an upset around 3rd or 4th round, especialy now with an injury maybe. He is probably more likely to go out inn a upset in the 3rd or 4th round than he is to beat any of the 3 favorites, let alone possibly all 3 to win the title.
Pulling out of Rome with an injury does not seem to bolster his chances either.
You seem to be taking offense and think people are dismissing Federer as a qualitiy clay courter. They are not, just realistically evaluating his chances as a 38 year old who has hardly done anything on clay the last 6 years. Seriously if you look over his clay results since then, nearly beating Thiem in a best of 3 is probably one of his top highlights since 2012. He is still a top 10 clay courter in the Open Era, and 3rd best of his era on clay, maybe even a case for 2nd until/if Djokovic wins a 2nd RG title. Nadal was a great grass courter on rye grass way back in 2006-2011 too, he still does not have a prayer at Wimbledon this year.