The EU election was much a protest vote as anything else.
I think the Tories and labour are too entrenched in certain areas of the country to not be forces. However, both will be damaged over this Brexit affair, and The Brexit Party got votes in many of the Labour and Tory areas that voted for these parties in the last general election.
Though the Brexit Party needs a long-term vision, or it will be UKIP 2.0. UKIP in many ways is now redundant, and Farage will be too if it doesn't further articulate its own vision and ideas. I don't think a general election will happen soon. May's successor would be foolish to do it, given the EU election result and how the public view the Tories in this Brexit affair. If I were Johnson, or McVey, or Raab, or whomever else, I would sign a deal with the EU, and ride things out until 2022. By then, which is a little time away, things may have calmed down, and if a good deal can be struck, then the Brexit Party/Farage would have their thunder stolen. His/their entire rationale now is to expose the Tories for their mismanagement, but a good deal and a thorough plan in education, healthcare, housing, transportation, etc. would dent them and maybe secure another term in office.
As for Labour, I think they are just as split on Brexit, hence why Corbyn hasn't been as strong on this issue, and why they too lost seats in the EU elections. Due to this, I believe May and Corbyn should have come to an agreement many months ago, and with their combined Whips, it would have been enough to pass through the government.
This should have been May's plan all along, and not call an election, or only consult Corbyn at the last minute.