
so you know two of their squad players and on that basis you dismiss everyone else (because you don't know them). Good logic, keep it up.
This season Rayo are quite shit, but still have
some good players like Trashorras, Embarba and Jozabed; also useful players like Javi Guerra, Iturra, Baena, Manucho and Bebé; and lastly some volatile players like Ebert and Pablo Hernández, who can have 1 brilliant game and then 10 games full of nothingness.
A far better question would be a team like Villarreal (or even Eibar or Las Palmas this season)...
I know they have four ex prem players in their squad. (Two of them combined to score against Barce the other day) I know those four players were poor premier league rejects. From there you can start to form an opinion.
Except that your evaluations of those players are incredibly simplistic foregoing loads of important factors. Both Bebé and Manucho barely even played for Utd, so how exactly are you comparing their performances? Manucho played 16 minutes (!) of Premier League football for Utd, played some cup games in which he scored, then went to Hull on loan where he scored 2 in 13 PL games. Then went to Spain where he's so far scored more than 5 league goals once (8 in 25 games for Valladolid in 2012/13). Bebé played 2 PL games for Utd and 7 in all comps, in which he scored twice! In La Liga he's scored the same amount of goals... in 45 games.
Not to mention you're not even compensating for the difference in a club the level of Utd, perennial title-contenders and one of the best on the continent at that time, compared to the level of the likes of Valladolid, Córdoba, Rayo... all relegation contenders and mid-table at most. The fact that they struggled to get game time for the former and not the latter says very little about the respective leagues they're in, only really about the level of these particular clubs.
Take the example of Arouna Koné: had a decent career in Belgium & Holland, then went to Sevilla where he was a laughing stock and scored a single La Liga goal in 4 years and 40 appearances. Then he moved to promoted side Levante and in he was immediately a starter and played 34 games scoring 15 goals. He went to similar side in Wigan the next season and scored 11 in 34 in the PL. Then he moved to Everton which was again a step up (similar to Sevila) and since then he's struggled getting games and scoring only sporadically. The level of club he was at impacted his goalscoring ability far more than the switch between leagues did.
In that sense, what Ighalo has done this season at Watford is a counter-example to yours that is a lot worse following your logic, because he actually got significant playing time in his 3 years at relegation side Granada and only needed half a PL season to score the same amount of goals for promoted Watford.
I'm sure you'll turn it into evidence of the PL's competitiveness somehow though...