I think there's alot more to take into consideration regarding international football other than club football hampering it.
International Football managers are incredibly poor, All the best managers are being coached by the club teams.
Too many international games, World Cup Qualifying, Euros Qualifying, Nations League Qualifying, Then going on the play in those tournaments, You also have so many Friendly games.
International Football is a very slow tempo in the majority of games compared to what we are used to watching every week, The international football is general is pretty poor standard, You've the bigger nations that aren't what they used to be and the smaller nations have improved somewhat and the games are now closer than previous years.
The atmosphere at games is poor.
Most people just don't want there players to get injured on international duty and return to there clubs.
Basically it boils down to everyone's loyalty and a large percentage will say club football. For me personally I'd rather City win a friendly in the USA than England win the Euros as I couldn't give a bollocks about England.