If trade deals were passed like legislation in a parliament or Congress, with time in committee and lots of room for individual legislators to add their input, there would be so much more corporate abuse it's not even funny. This would give a chance for every favored sector, major employer in a powerful legislator's district, company that the government favors at the moment etc. to add in clauses favoring them. Doing an up-or-down or vote actually greatly reduces pork.
>If it’s the EU sometimes national parliaments have no say
Yes, that is what the European Union is, by deliberate design. The individual countries voluntarily agreed to give up that power- if they didn't, they'd have been pushed around by China and the Trump administration. The EU is strength in size as a negotiating bloc, as a top 3 global economy. (Also, famously, countries can just leave the EU if they don't feel like it's a good deal)