You have spotted the inequality in the system. If the money is available to spend, the parties can choose to spend it on legal fees.
Those legal fees will be paid from the matrimonial pot as all income, assets and liabilities are joint until a court order is made splitting those items.
If you choose to self-represent, you are saving yourself and your spouse money. You could choose to engage a solicitor which will deplete the assets more quickly.
There are circumstances where the costs are treated differently. Firstly, if the assets are limited and one party has greater needs than the other, the person with the greater needs will receive what they need in priority to their spouse. In perverse situations, one party could receive all liquid assets and the other party could be saddled with all of the debt.
Another situation would be where a party makes an open offer that is rejected and the court goes on to make an order that reflected or betters that offer. The court may then decide that the costs incurred after the offer was made should be paid by the person who rejects the offer. In those circumstances they would bear their own costs and those of their spouse.
Where this occurs the parties state what their costs are and the judge will take those out of the calculations, make the order then add the post-offer costs liability to the rejecting party.
There are other ways of approaching orders for costs - there is no standard formula - but as costs orders are rarely made in family proceedings, they are applied in a myriad of different ways.
What happens if one party is running up legal costs at an incredible rate (or they and their solicitor claim to be incurring these costs)
You can bet your bottom dollar that what the solicitor puts on the Form H is the amount they are going to charge. Their client is the paying customer and being up front about how much the process is going to cost is the best way of extracting monies without demur.
Charles