I absolutely agree however I'd say the solution isn't to discard Baines and Williams, instead we should be looking to bring in a top dog CB to go next to Williams. Don't forget mate, this is a Euro semi-finalist - not to be sniffed at.
We get a lightning fast CB in next to him who doesn't have the positional sense as a beagle puppy (Funes Mori) and we have a back four that should be able to cope with everything within reason.
To me, and i'd never profess to knowing more than Koeman, we should have gone 3-5-2 against Spurs. That would have allowed Baines to have an advanced starting position to try and negate against Walker at source. If Baines was ever beaten in a foot race - not a stick to beat him with given Walker is lightning fast - we would have had a further hurdle for him with the left sided CB coming out to stop him.
Instead we flooded the centre of the park to accomodate Barry who, as much as I love him, is never the man to play vs Spurs with Alli / Dembele / Kane / Eriksson all buzzing around him.