Re: Not it isn't allowed under WTO rules at all.
No problem at all with the grammar.
The UK is a member of WTO
On leaving the EU, we are still a member of WTO.
We then find ourselves without agreed schedules, so need to submit these for WTO approval, as per the WTO rules. These will be reviewed in accordance with the rules of the WTO. Other countries may object, but fortunately, WTO is a rules based organisation, so the objections have to be based on something other than an attempt to gain an unfair advantage.
What you forget to mention is that proposed fast track schedules for the UK are also accompanied by the EU attempting to reduce the quantities listed under their schedule - the proposal is that the current EU schedules are divided between UK and EU (that's already agreed between UK and EU).
If you are correct that this somehow renders the UK not party to WTO, then the same logic means the EU is also no longer party to the WTO.
It's also a lot more likely that the UK will simply agree to up the quantities permitted under the UK schedules, thus immediately addressing the concerns raised by third party countries, than it is that the EU will agree to keep the quantities listed in its schedule unchanged following the UK departure.