I don't think so.
I don't know where Lasso is getting his "three exit polls" claim, unless he's talking about "private polls" conducted by his own campaign for P.R. purposes. In fact, there were only two non-partisan exit polls of the election: the Cedatos poll Lasso cites (which had him winning by 53.02% to 47.8%) and one by Perfiles de Opinión (which had Moreno winning by 52.2% to 47.8%). There were also two "rapid count" organizations conducting parallel counts to the official one: Participación Ciudadana had Moreno winning by 50.8% to 49.2%, while the other (the name of which organization I cannot find) called it Moreno 51.15%, Lasso 47.8%. According to Cuenca High Life, the English-language online newspaper for expats, "the OAS observers also made their own count which is similar to the official results."
There's a partial recount going on, as requested by Lasso; we'll see if it affects the result.
Did fraud effect the outcome? No one has come forward with solid evidence of systematic fraud as of yet. One can't entirely count it out; some skepticism is always justified when a close election is won by the incumbent party. But taking the results of polling as a whole, it seems as unreasonable to claim "obvious fraud" in this case as it does to assert that, if it wasn't for "massive voter fraud," Trump would have "clearly" won the popular vote last November.