Manual entry wins at low volume, and low volume is a real thing rather than an embarrassment. If you process a handful of document orders a month, a person doing it is cheaper, simpler and better than any software, and anyone telling you otherwise is selling something. It also wins on the truly unusual order, the one with a hand drawn diagram and a phone call attached, where judgement matters more than throughput.
EDI wins where it is mandated, which is most large retailers. If your buyer's compliance team says EDI 850, that is the specification and an EDI provider is the right supplier. EDI is also genuinely excellent at what it does: structured, acknowledged, auditable document exchange at volume. The reason it does not solve the whole problem is not a flaw in EDI, it is that most of your accounts will never be big enough to justify onboarding.
A custom build wins when your rules are strange enough that no product will encode them, and when you have engineers who will still be there in two years. If your order flow depends on allocation logic, contract terms or a legacy system nobody else integrates with, building may be the only path. Go in knowing that the extraction model is the small part and the long tail of formats is the large part.
Generic OCR wins when your inputs are consistent. If ninety percent of your documents come from a system that emits the same layout every time, a template based parser is fast, cheap and completely adequate. It stops winning the moment your senders stop agreeing with each other, which in wholesale is usually immediately.
Other App Store apps win when their core assumption matches your customers. A B2B portal is excellent for accounts that will log in, and many wholesalers should run one. The mistake is assuming every account will adopt it. Your largest, oldest customers are usually the least willing to change how they order, because their side of the process has a procurement system of its own.
LevelOps wins on the documents that survive all of the above: the emailed PDF, the spreadsheet with merged cells, the scan with a handwritten note in the margin, from the account who will not use your portal and will never do EDI. That is not a small remainder. For most wholesalers on Shopify it is the majority of accounts and a large share of order lines.