So many holes? According to fans or the team?
I don't think there are as many "holes" as some people believe. I think they have a lot of serviceable NFL players on defense, just not many star players.
I would take having the DEs as Selvie, Mincey and Crawford with all having gone through training camp and staying healthy during the season over Ware in and out of the lineup backed up by players that just signed few weeks earlier.
At 1-tech, I watch game footage of McClain and he is not a star, but it much much better than Hayden, IMO. Melton might not duplicate Hatcher's sack numbers, but he knows the defense which should help everybody around him.
Lee will be back and Holloman had a really good game in week 17 as MLB.
Carter either ups his game or is likely to get replaced by Holloman.
SLB is not a full time position (goes off the field in the nickel) and they have multiple options there. Whoever does not play WLB between Holloman and Carter, Wilber, and Durant.
Church is serviceable at one safety spot.
Wilcox has a lot of upside at the other safety spot and was playing well in the pre-season. He eventually just had to much to overcome. He was a rookie with only 1 year of experience playing defense, then his mother died and then he got injured. Everybody laughs, but Matt Johnson, Heath and Jakar Hamilton all have good physical ability. The odds are that 1 of 4 players will step up to be a decent option as the 2nd safety.
CB should be OK if they can improve the pass rush and get everybody more developed within the scheme. A healthy Claiborne is at a minimum, a quality 3rd CB. He is likely to be much better with more time in the scheme because he is a known slow learner.
Biggest issues, IMO:
Need an elite pass rushing DE, even if he's only a nickel pass rushing specialist.
Need depth at DT.
Need Lee to stay Healthy, but have options behind him.
Huge question mark at the 2nd Safety position, but have several options.