I am generally in favour some diy when it is easy, simple and safe. It can be a lot less bother than trying to organise a professional.
On the other hand, if it is important to get a consistent job or it needs scaffolding or whatever to be safe, then get a professional to do it once and right. The cost will be trivial compared a few months of the managing agent’s fee.
If the newbies were putting out feelers to see what support there was for going one way or the other, then perhaps they are doing the right thing?
As a member of the owners corp, why not just talk directly, frankly and openly about your concern with the managing agent. The agent will take direction from the committee but at least you will know if the agent could recommend and hire appropriately qualified and insured tradespeople.