Does authentic Italian tiramisu contain large amounts of espresso?

A typical tiramisu will serve a good number of people, so each serving is unlikely to have more than about a shot's worth of espresso. There's a limit to what the savoiardi will absorb so you'd struggle to get more coffee than that into a portion. Further, the flavour is diluted by the flavour already present in the savoiardi as well as the alcohol, mascarpone, cocoa on top and other ingredients. I wouldn't worry about the coffee flavour overpowering the rest. Obviously if you've made it before and felt the coffee was too strong then reduce the quantity.

Note that in Italy, caffè will by default refer to espresso, or at home to the product of a Moka pot or equivalent. Filter or drip coffees are not a native part of Italian coffee culture (hence the americano, imitating filter coffee by diluting espresso). You could search for older recipes in Italian (although according to Wikipedia, tiramisu is not an especially old dessert) but they will probably just say caffè.

Remember that tira mi sù means 'pick me up', alluding to the fact that the dessert contains enough coffee to wake you up a little at the end of a meal.

As a suppliment, I'll address your questions regarding "authenticity":

Tiramisu is not a traditional dish; it's a modern restaurant dish dating back only to the 1960's (but see other answer, it may go back to the 30s). It's generally agreed that it was created at the restaurant Le Beccherie in 1969 (although based on a long tradition of Italian cream cakes), so it's fairly easy to find their original recipe. This is it from a publication in 1981:

12 egg yolks

1 lb 2 oz (½ kg) sugar

2 lb 4 oz (1 kg) mascarpone cheese

60 ladyfinger (savoiardi) cookies

Espresso coffee, as necessary

Cocoa powder, as necessary

As you can see, no quantity for the espresso is given; likely the restaurant did not keep track of how much was used, particularly since they probably used "leftover" coffee from service. Interestingly, there is no alcohol in this version. Anna Maria Volpi, who is rather obsessed with the dish, uses 1.5 cups of espresso.

All of the advice in @dbmag9's excellent answer, therefore, applies.

There are in fact multiple versions of tiramisu, all of which are authentic. Some contain espresso and mascarpone, others cream, marsala but no mascarpone.

'Tiramisu' dates at least to the 1940s as a name, and to the 1930s as a recipe (much earlier considering related desserts)

Following documentary proof presented to the Italian government, the Protected Origin to the Friuli Venezia Giulia region was granted in 2017.

This has two forms:

1. tiramisu carnico - with mascarpone, attributed to Norma Pielli Hotel Roma Tolmezzo , and existing in the 1950s or earlier - recipe includes '300ml bitter and strong coffee' but no alcohol https://www.udinetoday.it/cucina/disciplinare-ricetta-tiramisu-signora-norma-pielli-tolmezzo.html
2. Coppa Vetturino Tirime su/tiramisu bisiacca - without mascarpone (instead cream) or espresso, and with marsala, by Mario Cosolo from Al Vetturino restaurant - recipe https://www.oggi.it/cucina/ricetta/tiramisu-della-tradizione-prima-coppa-vetturino-1935-1938-poi-tirimesu-1946-1950/

There are also:

1. Tiramisu Veneto from Le Beccherie, Treviso, made with mascarpone, coffee to taste and without alcohol https://www.informacibo.it/la-ricetta-originale-del-tiramisu-di-treviso/
2. Coppa Imperiale - from Ristorante Al Fogher, which is similar to the above and claims to predate it, but included a liqeur (possibly Grand Marnier) recipe https://www.hotelalfogher.it/restaurant.htm