There aren't a 'lot of signings elsewhere', at least not yet. I don't think anyone's suggested that yet. My own suggestion is that it's possible to do good business before tournaments like the Euros begin, and clubs have conducted such business already this close season, even with their great number and their shared, unfortunate handicap of not being Tottenham.
However, I don't particularly think waiting until after the Euros when the mad scramble begins anyway is a particularly well thought-out strategy if that's what we're doing by choice; seems somewhat backwards to me. If we're forced into it by top targets refusing to negotiate till after the Euros, fine, no problems with waiting (even if, as I mentioned, these tournaments should be factored into common transfer strategies by now; perhaps by adopting different approaches to players in off-seasons with international tournaments?). But doing it by choice? Nah, although fwiw, I don't think that's what we're aiming to do this summer, thankfully.
I don't really agree that doing your business early is overestimated as something that brings significant bonuses. Hits and misses aside, early transfers can be bedded into summer training, can get up to speed quicker, can sort out the off-the-pitch aspects of moving (perhaps to another country if they're coming from abroad) and settling in prior to the season beginning, and can be more fruitfully employed in terms of fitting into a team's overall plan as opposed to either being thrown in to real matches see where they fit or benched for the early part of the season while the manager decides where and how to deploy the player on the training field. To me, those are enormous advantages, especially given the emphasis on training and tactical understanding inherent in Bielsa-esque tactics like the ones Poch uses.