Looking at his record again, its pretty decent:
https://www.transfermarkt.co.uk/paulo-fonseca/leistungsdatenLigenNational/trainer/19944
In Portugal:
- 12/13 took a minnow team to 3rd. Excellent
- 13/14 had Porto in 3rd when sacked with > 2 points per game. 3rd is probably as low as they should be in their league, so not great but 1st season there
- 14/15 back to minnows and finished 1 point off 6th. Very good again
- 15/16: took Braga to 4th...in a league with Benfica, Sporting Lisbon and Porto so about as far as could realistic be expected
....so all that above bit looks very good then to Ukraine
16/17 to 18/19: cleaned up...obviously with the dominant team
then on to Italy:
19/20: finished 5th in his first season - pretty decent; I cant comment on level of spend in advance of that vs other teams, but 5th is probably par or slightly better with their status in Italy?
20/21: 7th, which is probably marginally sub-par, again with the transfer caveat
In Europe, he obviously made the EL semis with Roma and a couple QFs with Porto and Braga and some last 16s with Shaktar (CL) and Roma (EL)
So I think criticism of his record is probably a little harsh. I think a bigger concern that people could have is lack of familiarity with the PL. Personally I'd have probably gone for Potter rather than him, but as I've said many times, the DoF performance is far more important in my eyes over the next 12-24 months as without a couple decent summer windows, the coach is less relevant