son nobody in their right mind would discuss '06, that was a LOADED compe ion and even missi + spain wouldn't be clear cut winners. I wasn't even considering that tbh.
What I'm saying is that:
1) spain already has '08-'10-'12
2) '14 would've been winnable if del bosque didn't melt down after one loss in the confederations cup and went for a pivot like costa who didn't fit at all in that team and who killed their chemistry, tactics and long term strategy ... '14 was a huge blunder and it was ALL on del bosque for implementing a disfunctional system which didn't take into account spain's strengths. Just look at the games, they played a good amount of kick and run

. Case in point, as it was totally obvious that '14 had wrong tactics, in '16 they went back to their normal system but their lack of a true striker hurt them a lot, and lost a tough match against italy in a horror bracket, that's life at the euros tbh
You think they panic in '14 and play kick and run with messi?

, of course no, they play their normal game and instead of stagnating the offense when the other team defends with 11 people they'd open them up with quick messi combinations and isos. Which team could contend against them? bra7il? netherlands? germany? none comes close.
3) With messi they also get '16, they beat croatia and they go in the easy bracket and they slap france in the final.
4) And in '18 they might be old but they're still THE top contenders. Also look at our era, except spain we didn't get monster teams (the caliber of zidane france, italy '06, brasil '02) in over a decade, which a clear staple of Germany winning the world cup, otherwise we just lack the talent to go against the GOAT squads. Who would stop a GOAT squad these days? answer: nobody. Also I speak from national experience ('02,' 06, '08, '10) when I say that playing against a GOAT squad makes you nervous and error prone, so a GOAT squad has this advantage too.
Realistically speaking it is all very reasonable to say they'd win all of 08-18 tbh.