A great DT is not what leads a team to wins.
A great QB is.
And even Fisher himself said openly (and the amount of picks the Rams gave up to draft Goff graphically indicate) the need and value for a great QB. Without one, the chances of being a playoff team are slim.
I just don't think the Rams should pay what Donald wants. Wring the 2 years at current pay out of him; Franchise him twice, and then get what you can for him. What have teams that have paid the $80 - $100mil deals to DTs gotten out of it? It's the wrong place to spend big bucks.
Heck, Denver acquired an aging and nearly immobile Manning and paid him huge bucks. But that was worth the price: a Superbowl victory.