This is not a debate about which is better; it is a question of which suits your situation. There are scenarios in which each of them is the right answer.
When an off-the-shelf package (ERP, ready-made SaaS) is right: when your processes are standard and close to sector norms, when you want to start quickly, when keeping the initial investment low is your priority, and when you are willing to adapt your process to the software rather than the software to your process. The initial cost is low here; but per-user monthly or annual licensing, limited customisation and the cost of 'it doesn't quite fit my business' build up over time.
When custom software is right: when your competitive advantage lies in the process itself, when packages force you into their mould, when you want to escape licence costs that repeat across a large user base, and when you expect the software to grow with you for years. The initial investment is higher here; but the software is yours, there is no licence rent, and every screen is designed around your business.
The Pan approach: we do not make the decision for you. During discovery we listen to your processes and, where an off-the-shelf package would be enough, we say so honestly; where custom development genuinely adds value, we show you with numbers what we are recommending and why. Very often the right answer is a hybrid: modules specific to your business on top of a ready-made backbone.