It was hot, I walked late May until the beginning of July in 2017. That year we had a heatwave, and it was over 40 degrees when we reached Santiago.
I had somewhat acclimatized, as it was hot in May in NZ that year, and had been walking for a month by the time we reached Santiago. It was coolish in the mornings, but heated up a lot.
It was also extremely busy from Sarria, the only walk we have that busy is the Tongariro Crossing. where you can often see a conga line. Im not a fan of walking in such numbers, others dont mind it.
Its sort of like the beginning of a half marathon race, extremely congested at the beginning, and slowly spreads out.
If you haven't walked the rest of the Camino, you wouldn't know any different., I think its a shock when you've been walking in quiet country side for weeks on end, and then you hit the crowds.