Lifestyle funds, which automatically switch into lower-risk assets as you get older are the default option on PRSAs but you can choose to opt out and select your own funds if you wish.
On other forms of pension product, lifestyle funds are a choice so if you want your pension provider to manage your funds in this way, you have to proactively choose the lifestyle fund option. That assumes that your provider has a lifestyle fund option, or in this case, that they did have when your relative started his plan.
In my opinion, any complaint will revolve around what was documented at the time your relative started the plan. Did he specifically ask the pension provider to actively manage his pension fund and switch him into lower-risk funds as he approached retirement? Or did he assume that they would? If the latter, did they give him any assurances or reason to believe that they would do this?