I didn't read what roomey said as claiming the UK wasn't technically a net contributor. Just that it this fact is just a sliver of the entire picture, but was used heavily in pro-Brexit propaganda.
Indeed, the UK can now spend what they net contributed to the EU before. But I think it's doubtful that this makes up for everything else the UK lost in the process that isn't just some monetary number (in some government budget).
Things like the already mentioned access to the European research and university space - which hugely profited the UK because they used to be really good at "brain draining" the rest of the EU. Access to the European markets is now harder as well, translating directly to (at least in the short term) lost revenue and profit for UK companies, and lost tax revenue for the government, as well as some additional supply chain problems on top of the supply chain problems everybody else faces already.
The UK says their net contribution was "an average net contribution of £7.7 billion between 2014 and 2018". Of course this is only partially true. They got a lot more money back indirectly because they directly profited from some of the work various EU agencies did (and now they have to pay people to do the same work a lot of times). Some of these agencies were based in the UK, paid from the EU budget with individual employees paying taxes to the UK government. A lot of the university stuff (funding PhDs, Erasmus) is also not covered by their estimates (tho general research grants were). They lost access to EU funded research programs (like CERN or ITER), too, and now have to foot the bill to participate in those themselves, if they want and are allowed to still participate (e.g. ITER is not EU, and the UK will still participate, but where the EU previously paid a lot of the UK scientists and engineers out of their funds, now the UK government will have to pay them directly).
So I think their actual net contribution was more like 4-6 billion, and that doesn't still factor in lost opportunity costs due to now limited access to the European economic and labor markets, and the collective bargaining powers of the EU in things like trade deals, etc.
Given all that, I'd argue that there is ample reason to theorize Brexit was monetarily a net negative for the UK. It's hard to say yet, because the long and slow Brexit process took ages, everybody is still adopting, and it's therefore too early to have any reliable mid to long term numbers. And of course, the impact of COVID-19 makes it even harder to analyze just the Brexit outcomes.
So, back to topic, I would agree that at least the Brexit supporters who focused mainly on the net contributor thing (not all Brexit supporters operated that way) used it as propaganda - like the infamous red NHS bus - and not in a sound argument for their cause. They willfully ignored all the other things that would or could happen as a result of a Brexit.
Being able to pull from a Europe wide talant pool was a huge benefit to the UK and her universities.
So there was massive, irreplaceable benefits just for universities lost due to the Brexit project.
Along with that Brexit has cost the UK a ton of money.. this net contributer stuff was literal propaganda.
The UK is worse off now, with less funding to go around.