The fundamental of Lankan team is good. Here they are missing direction, more than any thing else. England at home is quite a decent ODI side, even 3 years back they made the CT final. But, this is a good English side at home - I am sure no one expected Lankans to stress England this level before the series.
I think, this series has shown two critical weaknesses in SRL side - one is universal & I wrote it several times - the game has gone to a batting shoot out, therefore the side having solid 50 overs of bowling will dominate the game. AUS is doing that because their No 8, 9, 10 & Jack makes the team on bowling merit, then can put combined 35/100 sort of batting stat. Even the recent resurgent WI team actually won 3 ODI against AUS/SAF with 40 specialist overs + Holder as 5th bowler, not 4th; in SRL standard he would be 1st or 2nd.
With just 1.5 bowlers, SRL 'll struggle against any decent side. But, still they are far professional side than what we are making off them - recently demolished Irish side at their place, because their limited attack wasn't exposed there. SRL must re-think their strategy of ODI - at least 40 genuine overs are must for them, rest 10 can be shared by bits & pieces, including Angelo. Even in England, their batting depth is underutilized, therefore I don't think they need that extra caution at 8, 9.
2nd is the leadership - finally I am done with Anjelo; he is almost at per with Azhar; almost, because unlike Azhar, as a player he'll be 1st name in the team list. This series could have been quite easily 2-1 in favor of SRL even with this attack. Anyone looking at the composition of England team should understand that it's a chasing unit - SRL with their attack decided to defend against a side having Plunket at 11. Not only SRL, when PAK 'll take on England, only chance with PAK fielding I see is to bowl first & be prepared to chase 300 against a limited English attack with very little penetration after 10-12 overs.
I still believe by 2019, SRL 'll put a decent side to WC. In last 4 years, they are the only side winning ODI series in AUS & England with this same bunch of players + couple of greats. This is a young side & already has recovered the loss of Sanga, Mahela & Dilshan in batting mostly - just missing the experience of those stalwarts. Chandimal as Captain & couple of genuine bowlers to add to the team, they'll do much better. Even a 3-2 loss to Aussies might take them to 4th or 5th spot in ranking, which I think they are quite capable of at home, if they can put 20 quality spin overs.