There are two components, the deal itself and the team direction.
The deal is a good length at a reasonable price for what he brings. So it's a good deal and well deserved for Byron.
In terms of direction it's a bit more puzzling. At 3.4m it's a sign that they see him as a 2nd liner more so then a 3rd liner who can step up and fill a hole in the top-6. That assessment is fine, but given the logjam at wing we already have I'm not sure about committing for 4 years.
In some ways it similar to Desharnais's deal in that it lacks planning. When Desharnais re-signed we had Plekanec still producing well, Eller showing a lot of progress, and Galchenyuk on the doorstep. It made no sense to make that long of a commitment given where we should've been moving towards.
It's similar now, the plan has to be Kotkaniemi and Poehling (Or whoever we draft this year) as our top-6 centers fairly soon. That means Drouin, Domi, Gallagher locking up 3 of the 4 top-6 wing spots. Locking up Byron for that 4th spot doesn't make a lot of sense when you have Lehkonen, Hudon, Sherbak pusing for bigger responsibility. They are going to need that spot to continue to develop. So it might make sense to have Byron around for a year or two, while we wait for our centers to develop, but beyond that there's not a lot of room. And although there's always the trade option at that time, in MB's own words, trades are hard. It's better to keep the flexibility of a shorter deal.