Sometimes Trainline* is cheaper than other split ticket booking engines which charge say a commission based on the amount saved by finding a split, which for some saves can be greater than the Trainline booking which which is capped at £2.79. It does however one of poorer split ticketing algorithms, so something like the forum's website will usually find a better split ticket arrangement to begin with. Overall though, I'd question whether split tickets are desirable for a lot of business journeys - I book them for my own company, yes, but there's a lot of business travellers taking flexible tickets, maybe because they don't know what time their meetings will finish, or they might decide to go out for drinks on the last day of a conference, etc.
I have no idea how Trainline's business offering differs from their competitors. I worked for an organisation who used them because you could do SSO with OIDC, require internal account codes when booking, generate reports, etc. I'm sure competitors offer similar features, but I don't know how they stack up, nor how pricing compares, in all honesty as I've never had to choose a train booking platform for a company!
If the organisation isn't doing a huge amount of train travel, then the odd £2 booking fee probably isn't that much of a concern in any case.
By all means if you think there's a way your organisation could save money, speak to whoever is in charge of procurement, but I'd stop short of overly-criticising the use of a particular platform until you know what they're getting out of it.
Trainline probably wouldn't be my choice, but like I say, I'd need to compare pricing as well as the features specific to the organisation's needs.
* by Trainline, I mean the website. They do of course power e.g. ScotRail's booking engine, which also offers split tickets, but doesn't charge a booking fee. ScotRail in this example also have a business offering, but I don't know if it's the same as Trainline Business.